Programming in C DaleWeemsHeadington Chapter 9 Additional Control

Programming in C++ Dale/Weems/Headington Chapter 9 Additional Control Structures (Switch, Do. . While, For statements) 1

Switch Statement Is a selection control structure for multi-way branching. SYNTAX switch ( Integral. Expression ) { case Constant 1 : Statement(s); case Constant 2 : Statement(s); . . . default : Statement(s); } // optional 2

float char weight. In. Pounds = 165. 8 ; weight. Unit ; . . . // user enters letter for desired weight. Unit switch ( weight. Unit ) { } case ‘P’ : case ‘p’ : cout << weight. In. Pounds << “ pounds “ << endl ; break ; case ‘O’ : case ‘o’ : cout << 16. 0 * weight. In. Pounds << “ ounces “ << endl ; break ; case ‘K’ : case ‘k’ : cout << weight. In. Pounds / 2. 2 << “ kilos “ << endl ; break ; case ‘G’ : case ‘g’ : cout << 454. 0 * weight. In. Pounds << “ grams “ << endl ; break ; default : cout << “That unit is not handled! “ << endl ; break ;

Switch Statement l The value of Integral. Expression (of char, short, int, long or enum type ) determines which branch is executed. l Case labels are constant ( possibly named ) integral expressions. Several case labels can precede a statement. 4

Control in Switch Statement l Control branches to the statement following the case label that matches the value of Integral. Expression. Control proceeds through all remaining statements, including the default, unless redirected with break. l If no case label matches the value of Integral. Expression, control branches to the default label, if present. Otherwise control passes to the statement following the entire switch statement. l Forgetting to use break can cause logical errors because after a branch is taken, control proceeds sequentially until either break or the end of the switch statement occurs. 5

Do-While Statement Is a looping control structure in which the loop condition is tested after each iteration of the loop. SYNTAX do { Statement } while ( Expression ) ; Loop body statement can be a single statement or a block. 6

Function Using Do-While void Get. Yes. Or. No ( /* out */ char& response ) // Inputs a character from the user // Postcondition: // response has been input && response == ‘y’ or ‘n’ { do { cin >> response ; // skips leading whitespace if ( ( response != ‘y’ ) && ( response != ‘n’ ) ) cout << “Please type y or n : “ ; } while ( ( response != ‘y’ ) && ( response != ‘n’ ) ) ; } 7

Do-While Loop vs. While Loop l l l POST-TEST loop (exit -condition) The looping condition is tested after executing the loop body. Loop body is always executed at least once. l l l PRE-TEST loop (entry-condition) The looping condition is tested before executing the loop body. Loop body may not be executed at all. 8

Do-While Loop DO Statement WHILE Expression TRUE FALSE When the expression is tested and found to be false, the loop is exited and control passes to the 9 statement that follows the do-while statement.

A Count-Controlled Loop SYNTAX for ( initialization ; test expression ; update ) { 0 or more statements to repeat } 10

The for loop contains an initialization an expression to test for continuing an update to execute after each iteration of the body 11

Example of Repetition int num; for ( num = 1 ; num <= 3 ; num++ ) { cout << num << “Potato” << endl; } 12

The output was: 1 Potato 2 Potato 3 Potato 13

What happens? l l l num is initialized to 1 expression num <= 3 is evaluated as true body is executed displaying 1 Potato update executed gives num value 2 expression num <= 3 is evaluated as true body is executed displaying 2 Potato update executed gives num value 3 expression num <= 3 is evaluated as true body is executed displaying 3 Potato update executed gives num value 4 expression num <= 3 is evaluated as false so loop ends 14

Count-controlled loop int count ; for ( count = 4 ; count > 0 ; count-- ) { cout << count << endl; } cout << “Done” << endl; OUTPUT: 4 3 2 1 Done 15

What is output? int count; for ( count = 0 ; count < 10 ; count++ ) { cout << “ ” ; } 16

OUTPUT ***** NOTE: the 10 asterisks are all on one line. Why? 17

What output from this loop? int count; for (count = 0; count < 10; count++) ; { cout << “ ” ; } 18

OUTPUT l l l No output from the for loop! Why? The ; right after the ( ) means that the body statement is a null statement In general, the Body of the for loop is whatever statement immediately follows the ( ) That statement can be a single statement, a block, or a null statement. Actually, the code outputs one * after the loop completes its counting to 10. 19

Several Statements in Body Block const int MONTHS = 12 ; int count ; float bill ; float sum = 0. 0 ; for (count = 1; count <= MONTHS; count++ ) { cout << “Enter bill: “ ; cin >> bill ; sum = sum + bill ; } cout << “Your total bill is : “ << sum << endl ; 20

Break Statement l Break statement can be used with Switch or any of the 3 looping structures. l It causes an immediate exit from the Switch, While, Do-While, or For statement in which it appears. l If the break is inside nested structures, control exits only the innermost structure containing it. 21

Continue Statement l Is valid only within loops. l Terminates the current loop iteration, but not the entire loop. l In a For or While, continue causes the rest of the body statement to be skipped. In a For statement, the update is done. l In a Do-While, the exit condition is tested, and if true, the next loop iteration is begun. 22

Imagine using. . . l a character, a length, and a width to draw a box. For example, l using the values ‘&’, 4, and 6 would display &&&&&& 23

Write prototype for void function called Draw. Box ( ) with 3 parameters. The first is type char, the other 2 are type int. void Draw. Box( char, int ); NOTE: Some C++ books include identifiers in prototypes. Any valid C++ identifiers, as long as each is different, can be used. void Draw. Box( char letter, int Num 1, int Num 2); 24

void Draw. Box(char What, int Down, int Across) // 3 formal parameters { int row, col; // 2 local variables for ( row = 0; row < Down; row++ ) { for (col = 0; col < Across; col++ ) { cout << What; } cout << endl; } return; }

THE DRIVER PROGRAM #include <iostream. h> void Draw. Box (char, int); // prototype int main (void) { char letter = ‘&’; Draw. Box(letter, 4, 2*3); Draw. Box(‘V’, 9, 3); return 0; // actual parameters // appear in call } 26