1 Lab 5 Pointers and Strings Outline 5

1 Lab 5 Pointers and Strings Outline 5. 1 5. 2 5. 3 5. 4 5. 5 5. 6 5. 7 5. 8 5. 9 5. 10 5. 11 5. 12 Introduction Pointer Variable Declarations and Initialization Pointer Operators Calling Functions by Reference Using const with Pointers Bubble Sort Using Pass-by-Reference Pointer Expressions and Pointer Arithmetic Relationship Between Pointers and Arrays of Pointers Case Study: Card Shuffling and Dealing Simulation Function Pointers Introduction to Character and String Processing 5. 12. 1 Fundamentals of Characters and Strings 5. 12. 2 String Manipulation Functions of the String. Handling Library 2004 Benjamin X. Wang All rights reserved.

2 5. 1 Introduction • Pointers – Powerful, but difficult to master – Simulate pass by reference – Close relationship with arrays and strings 2004 Benjamin X. Wang All rights reserved.

5. 2 3 Pointer Variable Declarations and Initialization • Pointer variables – Contain memory addresses as values – Normally, variable contains specific value (direct reference) – Pointers contain address of variable that has specific value count. Ptr (indirect reference) • Indirection 7 – Referencing value through pointer • Pointer declarations – * indicates variable is pointer int *my. Ptr; declares pointer to int, pointer of type int * – Multiple pointers require multiple asterisks int *my. Ptr 1, *my. Ptr 2; 2004 Benjamin X. Wang All rights reserved. count 7

5. 2 Pointer Variable Declarations and Initialization • Can declare pointers to any data type • Pointer initialization – Initialized to 0, NULL, or address • 0 or NULL points to nothing 2004 Benjamin X. Wang All rights reserved. 4

5 5. 3 Pointer Operators • & (address operator) – Returns memory address of its operand – Example int y = 5; int *y. Ptr; y. Ptr = &y; // y. Ptr gets address of y – y. Ptr “points to” y y. Ptr y 5 yptr 500000 600000 y 600000 address of y is value of yptr 2004 Benjamin X. Wang All rights reserved. 5

6 5. 3 Pointer Operators • * (indirection/dereferencing operator) – Returns synonym for object its pointer operand points to – *y. Ptr returns y (because y. Ptr points to y). – dereferenced pointer is lvalue *yptr = 9; // assigns 9 to y • * and & are inverses of each other 2004 Benjamin X. Wang All rights reserved.

1 2 3 // Fig. 5. 4: fig 05_04. cpp // Using the & and * operators. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 9 10 11 int main() { int a; int *a. Ptr; 12 13 14 a = 7; a. Ptr = &a; 15 16 17 cout << "The address of a is " << &a << "n. The value of a. Ptr is " << a. Ptr; 18 19 20 cout << "nn. The value of a is " << a << "n. The value of *a. Ptr is " << *a. Ptr; 21 22 23 24 cout << "nn. Showing that * and & are inverses of " << "each other. n&*a. Ptr = " << &*a. Ptr << "n*&a. Ptr = " << *&a. Ptr << endl; Outline // a is an integer // a. Ptr is a pointer to an integer // a. Ptr assigned address of a fig 05_04. cpp (1 of 2) * and & are inverses of each other 25 2004 Benjamin X. Wang All rights reserved. 7

26 27 28 return 0; // indicates successful termination Outline } // end main The address of a is 0012 FED 4 The value of a. Ptr is 0012 FED 4 The value of a is 7 The value of *a. Ptr is 7 Showing that * and & are inverses of each other. &*a. Ptr = 0012 FED 4 *&a. Ptr = 0012 FED 4 * and & are inverses; same result when both applied to a. Ptr fig 05_04. cpp (2 of 2) fig 05_04. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved. 8

9 5. 4 Calling Functions by Reference • 3 ways to pass arguments to function – Pass by value – Pass by reference with reference arguments – Pass by reference with pointer arguments • return can return one value from function • Arguments passed to function using reference arguments – Modify original values of arguments – More than one value “returned” 2004 Benjamin X. Wang All rights reserved.

10 5. 4 Calling Functions by Reference • Pass by reference with pointer arguments – Simulate pass by reference • Use pointers and indirection operator – Pass address of argument using & operator – Arrays not passed with & because array name already pointer – * operator used as alias/nickname for variable inside of function 2004 Benjamin X. Wang All rights reserved.

1 2 3 // Fig. 5. 6: fig 05_06. cpp // Cube a variable using pass-by-value. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 int cube. By. Value( int ); 9 10 11 12 int main() { int number = 5; Outline // prototype fig 05_06. cpp Pass number by value; result << number; (1 of 2) returned by cube. By. Value 13 14 cout << "The original value of number is " 15 16 17 // pass number by value to cube. By. Value number = cube. By. Value( number ); 18 19 cout << "n. The new value of number is " << number << endl; 20 21 return 0; 22 23 11 // indicates successful termination } // end main 24 2004 Benjamin X. Wang All rights reserved.

25 26 27 28 29 30 // calculate and return cube of integer argument int cube. By. Value( int n ) { cube. By. Value receives return n * n; // cube local variable n and return result Outline 12 parameter passed by value } // end function cube. By. Value The original value of number is 5 The new value of number is 125 Cubes and returns local variable n fig 05_06. cpp (2 of 2) fig 05_06. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

1 2 3 4 // Fig. 5. 7: fig 05_07. cpp // Cube a variable using pass-by-reference // with a pointer argument. #include <iostream> 5 6 7 using std: : cout; using std: : endl; 8 9 void cube. By. Reference( int * ); 10 11 12 13 int main() { int number = 5; Outline Prototype indicates parameter is pointer to int // prototype 14 15 cout << "The original value of number is " << number; 16 17 18 // pass address of number to cube. By. Reference( &number ); 19 20 cout << "n. The new value of number is " << number << endl; 21 22 return 0; 23 24 25 } // end main 13 Apply address operator & to pass address of number to cube. By. Reference // indicates successful termination fig 05_07. cpp (1 of 2) cube. By. Reference modified variable number 2004 Benjamin X. Wang All rights reserved.

26 27 28 29 30 31 // calculate cube of *n. Ptr; modifies variable number in main void cube. By. Reference( int *n. Ptr ) { *n. Ptr = *n. Ptr * *n. Ptr; // cube *n. Ptr } // end function cube. By. Reference The original value of number is 5 The new value of number is 125 Outline 14 cube. By. Reference receives address of int variable, i. e. , pointer to an int Modify and access int variable using indirection operator * fig 05_07. cpp (2 of 2) fig 05_07. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

15 5. 5 Using const with Pointers • const qualifier – Value of variable should not be modified – const used when function does not need to change a variable • Principle of least privilege – Award function enough access to accomplish task, but no more • Four ways to pass pointer to function – Nonconstant pointer to nonconstant data • Highest amount of access – Nonconstant pointer to constant data – Constant pointer to nonconstant data – Constant pointer to constant data • Least amount of access 2004 Benjamin X. Wang All rights reserved.

1 2 3 4 // Fig. 5. 10: fig 05_10. cpp // Converting lowercase letters to uppercase letters // using a non-constant pointer to non-constant data. #include <iostream> 5 6 7 using std: : cout; using std: : endl; 8 9 #include <cctype> 10 11 void convert. To. Uppercase( char * ); 12 13 14 15 int main() { char phrase[] = "characters and $32. 98"; // prototypes for Parameter is nonconstant pointer nonconstant data islower and to toupper fig 05_10. cpp (1 of 2) convert. To. Uppercase modifies variable phrase 16 17 18 19 20 cout << "The phrase before conversion is: " << phrase; convert. To. Uppercase( phrase ); cout << "n. The phrase after conversion is: " << phrase << endl; 21 22 return 0; 23 24 Outline 16 // indicates successful termination } // end main 25 2004 Benjamin X. Wang All rights reserved.

26 27 28 29 30 31 32 33 34 35 36 37 38 The // convert string to uppercase letters void convert. To. Uppercase( char *s. Ptr ) { while ( *s. Ptr != '' ) { // current character is not '' Outline 17 Parameter s. Ptr nonconstant ispointer lowercase, to nonconstant data if ( islower( *s. Ptr ) ) // if character *s. Ptr = toupper( *s. Ptr ); // convert to uppercase ++s. Ptr; Function islower returns // move s. Ptrtrue to next character if character is in string } // end while lowercase Function toupper returns } // end function convert. To. Uppercase corresponding When operatoruppercase ++ applied to character if original pointer that points tocharacter array, phrase before conversion is: characters and $32. 98 lowercase; otherwise memory address stored in phrase after conversion is: CHARACTERS AND $32. 98 toupper returnstooriginal pointer modified point to (uppercase) next elementcharacter of array. fig 05_10. cpp (2 of 2) fig 05_10. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

1 2 3 4 // Fig. 5. 11: fig 05_11. cpp // Printing a string one character at a time using // a non-constant pointer to constant data. #include <iostream> 5 6 7 using std: : cout; using std: : endl; 8 9 void print. Characters( const char * ); 10 11 12 13 int main() { Pass pointer char phrase[] = "print characters of a string" ; 14 15 16 17 cout << "The string is: n"; print. Characters( phrase ); cout << endl; 18 19 return 0; 20 21 Outline 18 Parameter is nonconstant pointer to constant data. phrase to function print. Characters. fig 05_11. cpp (1 of 2) // indicates successful termination } // end main 22 2004 Benjamin X. Wang All rights reserved.

23 24 25 26 27 28 // s. Ptr cannot modify the character to which it points, // i. e. , s. Ptr is a "read-only" pointer void print. Characters( const char *s. Ptr ) { for ( ; *s. Ptr != ''; s. Ptr++ ) // no initialization s. Ptr is nonconstant cout << *s. Ptr; 29 30 } // end function print. Characters The string is: print characters of a string pointer to constant data; cannot modify character to which s. Ptr points. Increment s. Ptr to point to next character. Outline 19 fig 05_11. cpp (2 of 2) fig 05_11. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

1 2 3 // Fig. 5. 12: fig 05_12. cpp // Attempting to modify data through a // non-constant pointer to constant data. 4 5 void f( const int * ); 6 7 8 9 int main() { int y; Outline 20 // prototype Parameter is nonconstant pointer to constant data. 10 11 f( &y ); // f attempts illegal modification 12 13 return 0; // indicates successful termination Pass address of int variable y to attempt illegal modification. 14 15 } // end main 16 17 18 19 20 21 // x. Ptr cannot modify the value of the variable Attempt to modify const // to which it points object pointed to by x. Ptr. void f( const int *x. Ptr ) { *x. Ptr = 100; // error: cannot modify a const object 22 23 } // end function f fig 05_12. cpp (1 of 1) fig 05_12. cpp output (1 of 1) Error produced when attempting to compile. d: Fig 05_12. cpp(21) : error C 2166: l-value specifies const object 2004 Benjamin X. Wang All rights reserved.

21 5. 5 Using const with Pointers • const pointers – Always point to same memory location – Default for array name – Must be initialized when declared 2004 Benjamin X. Wang All rights reserved.

1 2 3 // Fig. 5. 13: fig 05_13. cpp // Attempting to modify a constant pointer to // non-constant data. 4 5 6 7 int main() { int x, y; 8 9 10 11 12 ptrthat is constant pointer // ptr is a constant pointer to an integer can // be modified through ptr, but ptr always points integer. Can modify x (pointed to byto the // same memory location. ptr) since x not constant. Cannot modify ptr to point * const ptr = &x; 13 14 15 *ptr = 7; ptr = &y; // allowed: // error: ptr is const; cannot assign new address 16 17 return 0; // indicates successful 18 19 Outline to to new address since ptr is constant. *ptr is not const } // end main 22 Line 15 generates compiler error by attempting to assign termination new address to constant pointer. fig 05_13. cpp (1 of 1) fig 05_13. cpp output (1 of 1) d: Fig 05_13. cpp(15) : error C 2166: l-value specifies const object 2004 Benjamin X. Wang All rights reserved.

1 2 3 // Fig. 5. 14: fig 05_14. cpp // Attempting to modify a constant pointer to constant data. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 9 10 int main() { int x = 5, y; Outline 11 12 13 14 15 16 17 cout 18 19 20 *ptr = &y; value // error: ptr is const; cannot assign new address 21 22 return 0; // indicates successful termination 23 24 ptr is integer. constant pointer // ptr is a constant pointer to a constant integer the constant. // ptr always points to the same location; integer // at that location cannot be modified. const int *const ptr = &x; 23 to fig 05_14. cpp (1 of 1) Cannot modify x (pointed to by ptr)modify since *ptr declared Cannot ptr to point << *ptr << endl; constant. to new address since ptr is = 7; // error: *ptr constant. is const; cannot assign new } // end main 2004 Benjamin X. Wang All rights reserved.

d: Fig 05_14. cpp(19) : error C 2166: l-value specifies const object d: Fig 05_14. cpp(20) : error C 2166: l-value specifies const object Outline 24 Line 19 generates compiler error by attempting to modify Line 20 generates constant object. compiler error by attempting to assign new address to constant pointer. fig 05_14. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

25 5. 6 Bubble Sort Using Pass-by-Reference • Implement bubble. Sort using pointers – Want function swap to access array elements • Individual array elements: scalars – Passed by value by default • Pass by reference using address operator & 2004 Benjamin X. Wang All rights reserved.

1 2 3 4 // Fig. 5. 15: fig 05_15. cpp // This program puts values into an array, sorts the values into // ascending order, and prints the resulting array. #include <iostream> 5 6 7 using std: : cout; using std: : endl; 8 9 #include <iomanip> 10 11 using std: : setw; 12 13 14 void bubble. Sort( int *, const int ); void swap( int * const, int * const ); 15 16 17 18 19 int main() { const int array. Size = 10; int a[ array. Size ] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 }; // prototype 20 21 cout << "Data items in original ordern" ; 22 23 24 for ( int i = 0; i < array. Size; i++ ) cout << setw( 4 ) << a[ i ]; Outline 26 fig 05_15. cpp (1 of 3) 25 2004 Benjamin X. Wang All rights reserved.

26 bubble. Sort( a, array. Size ); 27 28 cout << "n. Data items in ascending ordern" ; 29 30 31 for ( int j = 0; j < array. Size; j++ ) cout << setw( 4 ) << a[ j ]; 32 33 cout << endl; 34 35 return 0; // sort the array // indicates successful termination 36 37 } // end main 38 39 40 41 42 43 // sort an array of integers using void bubble. Sort( int *array, const { // loop to control passes for ( int pass = 0; pass < size - 1; pass++ ) 44 45 46 47 48 49 50 Outline 27 Declare as int *array Receives size of array as declared const to (rather thanargument; int array[]) fig 05_15. cpp ensure size not modified. indicate function bubble to sort algorithm (2 of 3) bubble. Sort receives single int size ) subscripted array. // loop to control comparisons during each pass for ( int k = 0; k < size - 1; k++ ) // swap adjacent elements if they are out of order if ( array[ k ] > array[ k + 1 ] ) swap( &array[ k ], &array[ k + 1 ] ); 2004 Benjamin X. Wang All rights reserved.

51 52 53 54 55 56 57 58 59 60 61 62 Outline } // end function bubble. Sort 28 // swap values at memory locations to which // element 1 Ptr and element 2 Ptr point void swap( int * const element 1 Ptr, int * const element 2 Ptr ) { int hold = *element 1 Ptr; *element 1 Ptr = *element 2 Ptr; Pass *element 2 Ptr = hold; arguments by reference, allowing function to swap values at memoryfig 05_15. cpp locations. (3 of 3) } // end function swap Data items in original order 2 6 4 8 10 12 89 68 Data items in ascending order 2 4 6 8 10 12 37 45 45 37 68 89 fig 05_15. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

29 5. 6 Bubble Sort Using Pass-by-Reference • sizeof – Unary operator returns size of operand in bytes – For arrays, sizeof returns ( size of 1 element ) * ( number of elements ) – If sizeof( int ) = 4, then int my. Array[10]; cout << sizeof(my. Array); will print 40 • sizeof can be used with – Variable names – Type names – Constant values 2004 Benjamin X. Wang All rights reserved.

1 2 3 4 // Fig. 5. 16: fig 05_16. cpp // Sizeof operator when used on an array name // returns the number of bytes in the array. #include <iostream> 5 6 7 using std: : cout; using std: : endl; 8 9 size_t get. Size( double * ); 10 11 12 13 int main() { double array[ 20 ]; // prototype Operator sizeof applied to an array returns total number array is " of bytes in array. 14 15 16 cout << "The number of bytes in the << sizeof( array ); 17 18 19 cout << "n. The number of bytes returned by get. Size is " << get. Size( array ) << endl; 20 21 return 0; 22 23 24 } // end main Outline 30 fig 05_16. cpp (1 of 2) // indicates successful termination Function get. Size returns number of bytes used to store array address. 2004 Benjamin X. Wang All rights reserved.

25 26 27 28 // return size of ptr size_t get. Size( double *ptr ) { return sizeof( ptr ); 29 30 } // end function get. Size Outline 31 Operator sizeof returns 160 number of bytes of pointer. The number of bytes in the array is The number of bytes returned by get. Size is 4 fig 05_16. cpp (2 of 2) fig 05_16. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

1 2 3 // Fig. 5. 17: fig 05_17. cpp // Demonstrating the sizeof operator. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 9 10 11 12 13 14 15 16 17 18 int main() { char c; short s; int i; long l; float f; double d; long double ld; int array[ 20 ]; int *ptr = array; Outline 32 fig 05_17. cpp (1 of 2) 19 2004 Benjamin X. Wang All rights reserved.

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 cout << << << << << 37 38 return 0; 39 40 "sizeof c = " << sizeof c "tsizeof(char) = " << sizeof( char ) "nsizeof s = " << sizeof s Operator sizeof can be "tsizeof(short) = " << sizeof( short ) used on variable Operatorname. sizeof can be "nsizeof i = " << sizeof i used on type name. "tsizeof(int) = " << sizeof( int ) "nsizeof l = " << sizeof l "tsizeof(long) = " << sizeof( long ) "nsizeof f = " << sizeof f "tsizeof(float) = " << sizeof( float ) "nsizeof d = " << sizeof d "tsizeof(double) = " << sizeof( double ) fig 05_17. cpp "nsizeof ld = " << sizeof ld "tsizeof(long double) = " << sizeof( long double ) (2 of 2) "nsizeof array = " << sizeof array "nsizeof ptr = " << sizeof ptr endl; Outline 33 // indicates successful termination } // end main 2004 Benjamin X. Wang All rights reserved.

sizeof sizeof sizeof c = 1 sizeof(char) = 1 s = 2 sizeof(short) = 2 i = 4 sizeof(int) = 4 l = 4 sizeof(long) = 4 f = 4 sizeof(float) = 4 d = 8 sizeof(double) = 8 ld = 8 sizeof(long double) = 8 array = 80 ptr = 4 Outline 34 fig 05_17. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

35 5. 7 Pointer Expressions and Pointer Arithmetic • Pointer arithmetic – – Increment/decrement pointer (++ or --) Add/subtract an integer to/from a pointer( + or += , - or -=) Pointers may be subtracted from each other Pointer arithmetic meaningless unless performed on pointer to array • 5 element int array on a machine using 4 byte ints – v. Ptr points to first element v[ 0 ], which is at location 3000 v. Ptr = 3000 location – v. Ptr += 2; sets v. Ptr to 3008 v. Ptr points to v[ 2 ] 3000 3004 v[0] v[1] pointer variable v. Ptr 2004 Benjamin X. Wang All rights reserved. 3008 3012 v[2] 3016 v[3] v[4]

5. 7 Pointer Expressions and Pointer Arithmetic • Subtracting pointers – Returns number of elements between two addresses v. Ptr 2 = v[ 2 ]; v. Ptr = v[ 0 ]; v. Ptr 2 - v. Ptr == 2 • Pointer assignment – Pointer can be assigned to another pointer if both of same type – If not same type, cast operator must be used – Exception: pointer to void (type void *) • Generic pointer, represents any type • No casting needed to convert pointer to void pointer • void pointers cannot be dereferenced 2004 Benjamin X. Wang All rights reserved. 36

5. 7 Pointer Expressions and Pointer Arithmetic • Pointer comparison – Use equality and relational operators – Comparisons meaningless unless pointers point to members of same array – Compare addresses stored in pointers – Example: could show that one pointer points to higher numbered element of array than other pointer – Common use to determine whether pointer is 0 (does not point to anything) 2004 Benjamin X. Wang All rights reserved. 37

5. 8 Relationship Between Pointers and Arrays • Arrays and pointers closely related – Array name like constant pointer – Pointers can do array subscripting operations • Accessing array elements with pointers – Element b[ n ] can be accessed by *( b. Ptr + n ) • Called pointer/offset notation – Addresses • &b[ 3 ] same as b. Ptr + 3 – Array name can be treated as pointer • b[ 3 ] same as *( b + 3 ) – Pointers can be subscripted (pointer/subscript notation) • b. Ptr[ 3 ] same as b[ 3 ] 2004 Benjamin X. Wang All rights reserved. 38

1 2 // Fig. 5. 20: fig 05_20. cpp // Using subscripting and pointer notations with arrays. 3 4 #include <iostream> 5 6 7 using std: : cout; using std: : endl; 8 9 10 11 12 int main() { int b[] = { 10, 20, 30, 40 }; int *b. Ptr = b; // set b. Ptr to point to array b 13 14 15 16 // output array b using array subscript notation cout << "Array b printed with: n" << "Array subscript notationn" ; 17 18 19 for ( int i = 0; i < 4; i++ ) cout << "b[" << i << "] = " << b[ i ] << 'n'; 20 21 22 23 24 // output array b using the array name and // pointer/offset notation cout << "n. Pointer/offset notation where " << "the pointer is the array namen" ; Outline 39 fig 05_20. cpp (1 of 2) Using array subscript notation. 25 2004 Benjamin X. Wang All rights reserved.

26 27 28 for ( int offset 1 = 0; offset 1 < 4; offset 1++ ) cout << "*(b + " << offset 1 << ") = " << *( b + offset 1 ) << 'n'; 29 30 31 // output array b using b. Ptr and array subscript notation Using array name cout << "n. Pointer subscript notationn"; 32 33 34 for ( int j = 0; j < 4; j++ ) cout << "b. Ptr[" << j << "] = " << b. Ptr[ j ] << 'n'; 35 36 cout << "n. Pointer/offset notationn"; 37 38 39 40 41 // output array b using b. Ptr and pointer/offset notation for ( int offset 2 = 0; offset 2 < 4; offset 2++ ) cout << "*(b. Ptr + " << offset 2 << ") = " << *( b. Ptr + offset 2 ) << 'n'; 42 43 return 0; 44 45 Outline 40 and pointer/offset notation. } // end main Using pointer subscript notation. fig 05_20. cpp (2 of 2) // indicates successful termination Using b. Ptr and pointer/offset notation. 2004 Benjamin X. Wang All rights reserved.

Array b printed with: Outline 41 Array subscript notation b[0] = 10 b[1] = 20 b[2] = 30 b[3] = 40 Pointer/offset notation where the pointer is the array name *(b + 0) = 10 *(b + 1) = 20 *(b + 2) = 30 *(b + 3) = 40 Pointer b. Ptr[0] b. Ptr[1] b. Ptr[2] b. Ptr[3] fig 05_20. cpp output (1 of 1) subscript notation = 10 = 20 = 30 = 40 Pointer/offset notation *(b. Ptr + 0) = 10 *(b. Ptr + 1) = 20 *(b. Ptr + 2) = 30 *(b. Ptr + 3) = 40 2004 Benjamin X. Wang All rights reserved.

1 2 3 4 // Fig. 5. 21: fig 05_21. cpp // Copying a string using array notation // and pointer notation. #include <iostream> 5 6 7 using std: : cout; using std: : endl; 8 9 10 void copy 1( char *, const char * ); void copy 2( char *, const char * ); 11 12 13 14 15 16 17 int main() { char string 1[ 10 ]; char *string 2 = "Hello"; char string 3[ 10 ]; char string 4[] = "Good Bye"; Outline 42 // prototype 18 19 20 copy 1( string 1, string 2 ); cout << "string 1 = " << string 1 << endl; 21 22 23 copy 2( string 3, string 4 ); cout << "string 3 = " << string 3 << endl; 24 25 return 0; fig 05_21. cpp (1 of 2) // indicates successful termination 2004 Benjamin X. Wang All rights reserved.

26 27 } // end main 28 29 30 31 32 33 Use array subscript notation to // copy s 2 to s 1 using array notation copy string in s 2 to character void copy 1( char *s 1, const char *s 2 ) array s 1. { for ( int i = 0; ( s 1[ i ] = s 2[ i ] ) != ''; i++ ) ; // do nothing in body 34 35 } // end function copy 1 36 37 38 39 40 41 Use pointer notation to copy // copy s 2 to s 1 using pointer notation string void copy 2( char *s 1, const char *s 2 ) in s 2 to character array in s 1. { for ( ; ( *s 1 = *s 2 ) != ''; s 1++, s 2++ ) ; // do nothing in body 42 43 } // end function copy 2 string 1 = Hello string 3 = Good Bye Outline 43 fig 05_21. cpp (2 of 2) fig 05_21. cpp output (1 of 1) Increment both pointers to point to next elements in corresponding arrays. 2004 Benjamin X. Wang All rights reserved.

44 5. 9 Arrays of Pointers • Arrays can contain pointers – Commonly used to store array of strings char *suit[ 4 ] = {"Hearts", "Diamonds", "Clubs", "Spades" }; – Each element of suit points to char * (a string) – Array does not store strings, only pointers to strings suit[0] ’H’ ’e’ ’a’ ’r’ ’t’ ’s’ ’’ suit[1] ’D’ ’i’ ’a’ ’m’ ’o’ ’n’ ’d’ suit[2] ’C’ ’l’ ’u’ ’b’ ’s’ ’’ suit[3] ’S’ ’p’ ’a’ ’d’ ’e’ ’s’ ’’ – suit array has fixed size, but strings can be of any size 2004 Benjamin X. Wang All rights reserved.

45 5. 10 Case Study: Card Shuffling and Dealing Simulation • Card shuffling program – Use an array of pointers to strings, to store suit names – Use a double scripted array (suit by value) Ace 0 Hearts 0 Diamonds 1 Clubs 2 Spades 3 Two 1 Three Four 2 3 Five 4 Six 5 Seven Eight Nine 6 7 8 Ten 9 Jack 10 Queen King 11 12 deck[2][12] represents the King of Clubs King – Place 1 52 into the array to specify the order in which the cards are dealt 2004 Benjamin X. Wang All rights reserved.

5. 10 Case Study: Card Shuffling and Dealing Simulation • Pseudocode for shuffling and dealing simulation First refinement Initialize the suit array Initialize the face array Initialize the deck array Second refinement For each of the 52 cards Place card number in randomly selected unoccupied slot of deck 46 Third refinement Choose slot of deck randomly While chosen slot of deck has been previously chosen Choose slot of deck randomly Place card number in chosen slot of deck Shuffle the deck Deal 52 cards For each of the 52 cards Find card number in deck array and print face and suit of card 2004 Benjamin X. Wang All rights reserved. For each slot of the deck array If slot contains card number Print the face and suit of the card

1 2 3 // Fig. 5. 24: fig 05_24. cpp // Card shuffling dealing program. #include <iostream> 4 5 6 7 using std: : cout; using std: : left; using std: : right; 8 9 #include <iomanip> 10 11 using std: : setw; 12 13 14 #include <cstdlib> #include <ctime> 15 16 17 18 // prototypes void shuffle( int [][ 13 ] ); void deal( const int [][ 13 ], const char *[] ); 19 20 21 22 23 24 25 Outline fig 05_24. cpp (1 of 4) // prototypes for rand srand // prototype for time int main() suit array contains { to char arrays. // initialize suit array const char *suit[ 4 ] = { "Hearts", "Diamonds", "Clubs", "Spades" }; 47 pointers 2004 Benjamin X. Wang All rights reserved.

26 27 28 29 30 // initialize face array const char *face[ 13 ] = { "Ace", "Deuce", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King" }; 31 32 33 // initialize deck array int deck[ 4 ][ 13 ] = { 0 }; 34 35 srand( time( 0 ) ); 36 37 38 shuffle( deck ); deal( deck, face, suit ); 39 40 return 0; 41 42 Outline 48 face array contains pointers to char arrays. // seed random number generator fig 05_24. cpp (2 of 4) // indicates successful termination } // end main 43 2004 Benjamin X. Wang All rights reserved.

44 45 46 47 48 49 50 51 // shuffle cards in deck void shuffle( int w. Deck[][ 13 ] ) { int row; int column; // for each of the 52 cards, choose slot of deck randomly for ( int card = 1; card <= 52; card++ ) { 52 53 54 55 56 57 // choose new random location until unoccupied slot found Current position is at do { randomly selected row = rand() % 4; column = rand() % 13; } while ( w. Deck[ row ][ column ] != 0 ); // end do/while 58 59 60 // place card number in chosen slot of deck w. Deck[ row ][ column ] = card; 61 62 63 64 Outline 49 and fig 05_24. cpp (3 of 4) } // end for } // end function shuffle 65 2004 Benjamin X. Wang All rights reserved.

66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 // deal cards in deck void deal( const int w. Deck[][ 13 ], const char *w. Face[], const char *w. Suit[] ) { // for each of the 52 cards for ( int card = 1; card <= 52; card++ ) Outline 50 // loop through rows of w. Deck for ( int row = 0; row <= 3; row++ ) // loop through columns of w. Deck for current row for ( int column = 0; column <= 12; column++ ) // if Cause face to be output right fig 05_24. cpp Cause suit to beofoutput justified in field 5 (4 ofleft if slot contains current card, display card 4) justified in field of 8 characters. ( w. Deck[ row ][ column ] == card ) { characters. cout << setw( 5 ) << right << w. Face[ column ] << " of " << setw( 8 ) << left << w. Suit[ row ] << ( card % 2 == 0 ? 'n' : 't' ); } // end if } // end function deal 2004 Benjamin X. Wang All rights reserved.

Nine Five Queen Jack Three Ten Ace Seven Six Ace Nine Six Ten Four Ten Eight Jack Four Seven Queen Nine Deuce King Queen Five of of of of of of of Spades Diamonds Clubs Hearts Spades Hearts Clubs Hearts Spades Clubs Hearts Diamonds Hearts Spades Clubs Hearts Seven Eight Three Five Three Six Nine Queen Deuce Seven Eight King Ace Four Eight Ten King Four Six Jack Three Five Ace of of of of of of of Clubs Hearts Diamonds Clubs Diamonds Hearts Spades Clubs Diamonds Hearts Spades Diamonds Spades Hearts Diamonds Clubs Spades Clubs Diamonds Outline 51 fig 05_24. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

52 5. 11 Function Pointers • Pointers to functions – Contain address of function – Similar to how array name is address of first element – Function name is starting address of code that defines function • Function pointers can be – – Passed to functions Returned from functions Stored in arrays Assigned to other function pointers 2004 Benjamin X. Wang All rights reserved.

53 5. 11 Function Pointers • Calling functions using pointers – Assume parameter: • bool ( *compare ) ( int, int ) – Execute function with either • ( *compare ) ( int 1, int 2 ) – Dereference pointer to function to execute OR • compare( int 1, int 2 ) – Could be confusing • User may think compare name of actual function in program 2004 Benjamin X. Wang All rights reserved.

1 2 3 // Fig. 5. 25: fig 05_25. cpp // Multipurpose sorting program using function pointers. #include <iostream> 4 5 6 7 using std: : cout; using std: : cin; using std: : endl; 8 9 #include <iomanip> 10 11 using std: : setw; 12 13 14 15 16 17 // prototypes void bubble( int [], const int, bool (*)( int, int ) ); void swap( int * const, int * const ); bool ascending( int, int ); bool descending( int, int ); 18 19 20 21 22 23 24 int main() { const int array. Size = 10; int order; int counter; int a[ array. Size ] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 }; Outline 54 Parameter is pointer to function that receives two integer parameters and returns fig 05_25. cpp bool result. (1 of 5) 25 2004 Benjamin X. Wang All rights reserved.

26 27 28 29 30 31 32 33 cout << "Enter 1 to sort in ascending order, n" << "Enter 2 to sort in descending order: " ; cin >> order; cout << "n. Data items in original ordern" ; Outline 55 // output original array for ( counter = 0; counter < array. Size; counter++ ) cout << setw( 4 ) << a[ counter ]; 34 35 36 37 38 39 40 // sort array in ascending order; pass function ascending // as an argument to specify ascending sorting order if ( order == 1 ) { bubble( a, array. Size, ascending ); cout << "n. Data items in ascending ordern" ; } 41 42 43 44 45 46 47 // sort array in descending order; pass function descending // as an agrument to specify descending sorting order else { bubble( a, array. Size, descending ); cout << "n. Data items in descending ordern" ; } fig 05_25. cpp (2 of 5) 48 2004 Benjamin X. Wang All rights reserved.

49 50 51 // output sorted array for ( counter = 0; counter < array. Size; counter++ ) cout << setw( 4 ) << a[ counter ]; 52 53 cout << endl; 54 55 return 0; // indicates successful termination 56 57 } // end main 58 59 60 61 62 63 64 65 // multipurpose bubble sort; parameter compare is a pointer to functionorder that receives two // the comparison function that determines sorting integer parameters and returns void bubble( int work[], const int size, bool (*compare)( int, int ) ) bool result. { // loop to control passes Parentheses necessary to for ( int pass = 1; pass < size; pass++ ) 66 67 68 69 70 71 72 Outline 56 compare is pointer to fig 05_25. cpp (3 of 5) indicate pointer to function // loop to control number of comparisons per pass Call- passed function for ( int count = 0; count < size 1; count++ ) compare; dereference pointer execute function. out of to order, swap them // if adjacent elements are if ( (*compare)( work[ count ], work[ count + 1 ] ) ) swap( &work[ count ], &work[ count + 1 ] ); 2004 Benjamin X. Wang All rights reserved.

73 74 } // end function bubble 75 76 77 78 79 80 81 82 // swap values at memory locations to which // element 1 Ptr and element 2 Ptr point void swap( int * const element 1 Ptr, int * const element 2 Ptr ) { int hold = *element 1 Ptr; *element 1 Ptr = *element 2 Ptr; *element 2 Ptr = hold; 83 84 } // end function swap 85 86 87 88 89 90 91 92 // determine whether elements are out of order // for an ascending order sort bool ascending( int a, int b ) { return b < a; // swap if b is less than a Outline 57 fig 05_25. cpp (4 of 5) } // end function ascending 93 2004 Benjamin X. Wang All rights reserved.

94 95 96 97 98 99 100 // determine whether elements are out of order // for a descending order sort bool descending( int a, int b ) { return b > a; // swap if b is greater than a Outline 58 } // end function descending Enter 1 to sort in ascending order, Enter 2 to sort in descending order: 1 Data items in original order 2 6 4 8 10 12 89 68 Data items in ascending order 2 4 6 8 10 12 37 45 45 37 68 89 fig 05_25. cpp (5 of 5) fig 05_25. cpp output (1 of 1) Enter 1 to sort in ascending order, Enter 2 to sort in descending order: 2 Data items in original order 2 6 4 8 10 12 89 68 Data items in descending order 89 68 45 37 12 10 8 6 45 37 4 2 2004 Benjamin X. Wang All rights reserved.

59 5. 11 Function Pointers • Arrays of pointers to functions – Menu driven systems – Pointers to each function stored in array of pointers to functions • All functions must have same return type and same parameter types – Menu choice subscript into array of function pointers 2004 Benjamin X. Wang All rights reserved.

1 2 3 // Fig. 5. 26: fig 05_26. cpp // Demonstrating an array of pointers to functions. #include <iostream> 4 5 6 7 using std: : cout; using std: : cin; using std: : endl; 8 9 10 11 12 // function prototypes void function 1( int ); void function 2( int ); void function 3( int ); 13 14 15 16 17 18 int main() Array initialized with names { of threethat functions; // initialize array of 3 pointers to functions each function // take an int argument and return void names are pointers. void (*f[ 3 ])( int ) = { function 1, function 2, function 3 }; 19 20 int choice; 21 22 23 cout << "Enter a number between 0 and 2, 3 to end: " ; cin >> choice; Outline 60 fig 05_26. cpp (1 of 3) 24 2004 Benjamin X. Wang All rights reserved.

25 26 // process user's choice while ( choice >= 0 && choice < 3 ) { 27 28 29 30 // invoke function at location choice in array f // and pass choice as an argument (*f[ choice ])( choice ); 31 32 33 34 } 35 36 cout << "Program execution 37 38 Outline 61 cout << "Enter a number between 0 and 2, 3 to end: " ; cin >> choice; return 0; Call chosen function by dereferencing corresponding completed. " element<<inendl; array. // indicates successful termination 39 40 } // end main 41 42 43 44 45 void function 1( int a ) { cout << "You entered " << a << " so function 1 was callednn" ; 46 47 } // end function 1 fig 05_26. cpp (2 of 3) 48 2004 Benjamin X. Wang All rights reserved.

49 50 51 52 void function 2( int b ) { cout << "You entered " << b << " so function 2 was callednn" ; 53 54 } // end function 2 55 56 57 58 59 void function 3( int c ) { cout << "You entered " << c << " so function 3 was callednn" ; 60 61 } // end function 3 Enter a number between 0 and 2, 3 to end: 0 You entered 0 so function 1 was called Outline 62 fig 05_26. cpp (3 of 3) fig 05_26. cpp output (1 of 1) Enter a number between 0 and 2, 3 to end: 1 You entered 1 so function 2 was called Enter a number between 0 and 2, 3 to end: 2 You entered 2 so function 3 was called Enter a number between 0 and 2, 3 to end: 3 Program execution completed. 2004 Benjamin X. Wang All rights reserved.

5. 12. 1 Fundamentals of Characters and Strings • Character constant – Integer value represented as character in single quotes – 'z' is integer value of z • 122 in ASCII • String – Series of characters treated as single unit – Can include letters, digits, special characters +, -, *. . . – String literal (string constants) • Enclosed in double quotes, for example: "I like C++" – Array of characters, ends with null character '' – String is constant pointer • Pointer to string’s first character – Like arrays 2004 Benjamin X. Wang All rights reserved. 63

5. 12. 1 Fundamentals of Characters and Strings • String assignment – Character array • char color[] = "blue"; – Creates 5 element char array color • last element is '' – Variable of type char * • char *color. Ptr = "blue"; – Creates pointer color. Ptr to letter b in string “blue” • “blue” somewhere in memory – Alternative for character array • char color[] = { ‘b’, ‘l’, ‘u’, ‘e’, ‘’ }; 2004 Benjamin X. Wang All rights reserved. 64

5. 12. 1 Fundamentals of Characters and Strings • Reading strings – Assign input to character array word[ 20 ] cin >> word • Reads characters until whitespace or EOF • String could exceed array size cin >> setw( 20 ) >> word; • Reads 19 characters (space reserved for '') 2004 Benjamin X. Wang All rights reserved. 65

5. 12. 1 Fundamentals of Characters and Strings • cin. getline – Read line of text – cin. getline( array, size, delimiter ); – Copies input into specified array until either • One less than size is reached • delimiter character is input – Example char sentence[ 80 ]; cin. getline( sentence, 80, 'n' ); 2004 Benjamin X. Wang All rights reserved. 66

5. 12. 2 String Manipulation Functions of the String-handling Library • String handling library <cstring> provides functions to – – Manipulate string data Compare strings Search strings for characters and other strings Tokenize strings (separate strings into logical pieces) 2004 Benjamin X. Wang All rights reserved. 67

5. 12. 2 String Manipulation Functions of the String-handling Library char *strcpy( char *s 1, const char *s 2 ); Copies the string s 2 into the character array s 1. The value of s 1 is returned. char *strncpy( char *s 1, const char *s 2, size_t n ); Copies at most n characters of the string s 2 into the character array s 1. The value of s 1 is returned. char *strcat( char *s 1, const char *s 2 ); Appends the string s 2 to the string s 1. The first character of s 2 overwrites the terminating null character of s 1. The value of s 1 is returned. char *strncat( char *s 1, const char *s 2, size_t n ); Appends at most n characters of string s 2 to string s 1. The first character of s 2 overwrites the terminating null character of s 1. The value of s 1 is returned. int strcmp( const char *s 1, const char *s 2 ); Compares the string s 1 with the string s 2. The function returns a value of zero, less than zero or greater than zero if s 1 is equal to, less than or greater than s 2, respectively. 2004 Benjamin X. Wang All rights reserved. 68

5. 12. 2 String Manipulation Functions of the String-handling Library int strncmp( const char *s 1, const char *s 2, size_t n ); Compares up to n characters of the string s 1 with the string s 2. The function returns zero, less than zero or greater than zero if s 1 is equal to, less than or greater than s 2, respectively. char *strtok( char *s 1, const char *s 2 ); A sequence of calls to strtok breaks string s 1 into “tokens”—logical pieces such as words in a line of text—delimited by characters contained in string s 2. The first call contains s 1 as the first argument, and subsequent calls to continue tokenizing the same string contain NULL as the first argument. A pointer to the current to ken is returned by each call. If there are no more tokens when the function is called, NULL is returned. size_t strlen( const char *s ); Determines the length of string s. The number of characters preceding the terminating null character is returned. 2004 Benjamin X. Wang All rights reserved. 69

5. 12. 2 String Manipulation Functions of the String-handling Library • Copying strings – char *strcpy( char *s 1, const char *s 2 ) • Copies second argument into first argument – First argument must be large enough to store string and terminating null character – char *strncpy( char *s 1, const char *s 2, size_t n ) • Specifies number of characters to be copied from string into array • Does not necessarily copy terminating null character 2004 Benjamin X. Wang All rights reserved. 70

1 2 3 // Fig. 5. 28: fig 05_28. cpp // Using strcpy and strncpy. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 #include <cstring> 9 10 11 12 13 14 int main() { char x[] = "Happy Birthday to You"; Copy entire string char y[ 25 ]; into array y. char z[ 15 ]; 15 16 17 18 19 20 21 22 23 24 25 strcpy( y, x ); Outline 71 <cstring> contains prototypes for strcpy and strncpy. // prototypes for strcpy and strncpy in array x fig 05_28. cpp (1 of 2) // copy contents of x into y cout << "The string in array x is: " << x 14 characters << "n. The string in array y is: " Copy << y first << 'n'; of array x into array Append terminating nully. Note that // copy first 14 characters of x into zthis does not write terminating character. strncpy( z, x, 14 ); // does not copy null character. z[ 14 ] = ''; // append '' to z's contents cout << "The string in array z is: " << z << endl; 2004 Benjamin X. Wang All rights reserved.

26 27 28 29 return 0; // indicates successful termination } // end main The string in array x is: Happy Birthday to You The string in array y is: Happy Birthday to You The string in array z is: Happy Birthday Outline 72 String to copy. Copied string using strcpy. Copied first 14 characters using strncpy. fig 05_28. cpp (2 of 2) fig 05_28. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

5. 12. 2 String Manipulation Functions of the String-handling Library • Concatenating strings – char *strcat( char *s 1, const char *s 2 ) • Appends second argument to first argument • First character of second argument replaces null character terminating first argument • Ensure first argument large enough to store concatenated result and null character – char *strncat( char *s 1, const char *s 2, size_t n ) • Appends specified number of characters from second argument to first argument • Appends terminating null character to result 2004 Benjamin X. Wang All rights reserved. 73

1 2 3 // Fig. 5. 29: fig 05_29. cpp // Using strcat and strncat. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 #include <cstring> 9 10 11 12 13 14 int main() { char s 1[ 20 ] = "Happy "; char s 2[] = "New Year "; char s 3[ 40 ] = ""; Outline 74 <cstring> contains prototypes for strcat and strncat. // prototypes for strcat and strncat fig 05_29. cpp (1 of 2) Append s 2 to s 1. 15 16 cout << "s 1 = " << s 1 << "ns 2 = " << s 2; 17 18 strcat( s 1, s 2 ); 19 20 21 cout << "nn. After strcat(s 1, s 2): ns 1 = " << s 1 Append first 6 characters << "ns 2 = " << s 2; 22 23 24 // concatenate first 6 characters of s 1 to s 3 strncat( s 3, s 1, 6 ); // places '' after last character // concatenate s 2 to s 1 of s 1 to s 3. 25 2004 Benjamin X. Wang All rights reserved.

26 27 cout << "nn. After strncat(s 3, s 1, 6): ns 1 = " << s 1 Append s 1 to s 3. << "ns 3 = " << s 3; 28 29 30 31 strcat( s 3, s 1 ); // concatenate s 1 to s 3 cout << "nn. After strcat(s 3, s 1): ns 1 = " << s 1 << "ns 3 = " << s 3 << endl; 32 33 return 0; 34 35 Outline 75 // indicates successful termination } // end main s 1 = Happy s 2 = New Year After strcat(s 1, s 2): s 1 = Happy New Year s 2 = New Year fig 05_29. cpp (2 of 2) fig 05_29. cpp output (1 of 1) After strncat(s 3, s 1, 6): s 1 = Happy New Year s 3 = Happy After strcat(s 3, s 1): s 1 = Happy New Year s 3 = Happy New Year 2004 Benjamin X. Wang All rights reserved.

5. 12. 2 String Manipulation Functions of the String-handling Library • Comparing strings – Characters represented as numeric codes • Strings compared using numeric codes – Character codes / character sets • ASCII – “American Standard Code for Information Interchage” • EBCDIC – “Extended Binary Coded Decimal Interchange Code” 2004 Benjamin X. Wang All rights reserved. 76

5. 12. 2 String Manipulation Functions of the String-handling Library • Comparing strings – int strcmp( const char *s 1, const char *s 2 ) • Compares character by character • Returns – Zero if strings equal – Negative value if first string less than second string – Positive value if first string greater than second string – int strncmp( const char *s 1, const char *s 2, size_t n ) • Compares up to specified number of characters • Stops comparing if reaches null character in one of arguments 2004 Benjamin X. Wang All rights reserved. 77

1 2 3 // Fig. 5. 30: fig 05_30. cpp // Using strcmp and strncmp. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 #include <iomanip> 9 10 using std: : setw; 11 12 #include <cstring> 13 14 15 16 17 18 19 20 21 22 23 24 25 Outline <cstring> contains prototypes for strcmp and strncmp. // prototypes for strcmp and strncmp int main() { char *s 1 = "Happy New Year"; char *s 2 = "Happy New Year"; char *s 3 = "Happy Holidays"; cout << << << 78 "s 1 = " << s 1 << "ns 2 = " << s 2 Compare s 1 "ns 3 = " << s 3 << "nnstrcmp(s 1, s 2) = " setw( 2 ) << strcmp( s 1, s 2 ) "nstrcmp(s 1, s 3) = " << setw( 2 ) strcmp( s 1, s 3 ) << "nstrcmp(s 3, s 1) = " setw( 2 ) << strcmp( s 3, s 1 ); fig 05_30. cpp (1 of 2) Compare s 1 and s 2. and s 3. Compare s 3 and s 1. 2004 Benjamin X. Wang All rights reserved.

Compare up to 6 characters of Compare "nnstrncmp(s 1, s 3, 6) = " <<s 1 setw( 2 ) up to 7 characters of and s 3. s 1 and s 3. strncmp( s 1, s 3, 6 ) << "nstrncmp(s 1, s 3, 7) = " Compare up to 7 characters of setw( 2 ) << strncmp( s 1, s 3, 7 ) s 3 and s 1. "nstrncmp(s 3, s 1, 7) = " 26 27 28 29 30 31 cout << << << setw( 2 ) << strncmp( s 3, s 1, 7 ) << endl; 32 33 return 0; 34 35 Outline 79 // indicates successful termination } // end main s 1 = Happy New Year s 2 = Happy New Year s 3 = Happy Holidays strcmp(s 1, s 2) = 0 strcmp(s 1, s 3) = 1 strcmp(s 3, s 1) = -1 fig 05_30. cpp (2 of 2) fig 05_30. cpp output (1 of 1) strncmp(s 1, s 3, 6) = 0 strncmp(s 1, s 3, 7) = 1 strncmp(s 3, s 1, 7) = -1 2004 Benjamin X. Wang All rights reserved.

5. 12. 2 String Manipulation Functions of the String-handling Library • Tokenizing – Breaking strings into tokens, separated by delimiting characters – Tokens usually logical units, such as words (separated by spaces) – "This is my string" has 4 word tokens (separated by spaces) – char *strtok( char *s 1, const char *s 2 ) • Multiple calls required – First call contains two arguments, string to be tokenized and string containing delimiting characters • Finds next delimiting character and replaces with null character – Subsequent calls continue tokenizing • Call with first argument NULL 2004 Benjamin X. Wang All rights reserved. 80

1 2 3 // Fig. 5. 31: fig 05_31. cpp // Using strtok. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 #include <cstring> 9 10 11 12 13 int main() { char sentence[] = "This is a sentence with 7 tokens" ; char *token. Ptr; Outline 81 <cstring> contains prototype for strtok. // prototype for strtok 14 15 16 cout << "The string to be tokenized is: n" << sentence First call to strtok begins << "nn. The tokens are: nn"; 17 18 19 // begin tokenization of sentence token. Ptr = strtok( sentence, " " ); fig 05_31. cpp (1 of 2) tokenization. 2004 Benjamin X. Wang All rights reserved.

21 22 23 24 // continue tokenizing sentence until token. Ptr becomes NULL while ( token. Ptr != NULL ) { cout << token. Ptr << 'n'; token. Ptr = strtok( NULL, " " ); // get next token 25 26 } // end while 27 28 cout << "n. After strtok, sentence = " << sentence << endl; 29 30 return 0; 31 32 } // end main // indicates successful Outline 82 Subsequent calls to strtok with NULL as first argument to indicate continuation. termination fig 05_31. cpp (2 of 2) 2004 Benjamin X. Wang All rights reserved.

The string to be tokenized is: This is a sentence with 7 tokens Outline 83 The tokens are: This is a sentence with 7 tokens After strtok, sentence = This fig 05_31. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.

5. 12. 2 String Manipulation Functions of the String-handling Library • Determining string lengths – size_t strlen( const char *s ) • Returns number of characters in string – Terminating null character not included in length 2004 Benjamin X. Wang All rights reserved. 84

1 2 3 // Fig. 5. 32: fig 05_32. cpp // Using strlen. #include <iostream> 4 5 6 using std: : cout; using std: : endl; 7 8 #include <cstring> 9 10 11 12 13 14 int main() { char *string 1 = "abcdefghijklmnopqrstuvwxyz "; char *string 2 = "four"; char *string 3 = "Boston"; 15 16 17 18 19 20 21 cout << << << 22 23 return 0; 24 25 Outline 85 <cstring> contains prototype for strlen. // prototype for strlen "The length of "" << string 1 "" is " << strlen( string 1 ) "n. The length of "" << string 2 "" is " << strlen( string 2 ) "n. The length of "" << string 3 "" is " << strlen( string 3 ) << endl; fig 05_32. cpp (1 of 1) Using strlen to determine length of strings. // indicates successful termination } // end main 2004 Benjamin X. Wang All rights reserved.

The length of "abcdefghijklmnopqrstuvwxyz " is 26 The length of "four" is 4 The length of "Boston" is 6 Outline 86 fig 05_32. cpp output (1 of 1) 2004 Benjamin X. Wang All rights reserved.