Programming in C DaleWeemsHeadington Chapter 14 Records C

Programming in C++ Dale/Weems/Headington Chapter 14 Records ( C++ Structs ) 1

C++ Data Types Simple Structured Integral Floating array struct union class char short int long enum float double long double Address pointer reference 2

Limitation of array type In an array all elements (components) must be of the same type. For example, 20 chars or 52 floats or 100 strings. l Often we have related information of various types that we’d like to store together for convenient access under the same identifier. For example. . . 3

another. Animal 6000. id 5281003 . name ‘l’ ‘a’ ‘m’ ‘a’ ‘’ . . genus ‘L’ ‘a’ ‘m’ ‘a’ ‘’ . . species ‘p’ ‘e’ ‘r‘ ‘u’ ‘a’ ‘n’ ‘a’ ‘’ . . country ‘P’ ‘e’ ‘r‘ ‘u’ ‘’ . . age 7 . weight 278. 5 . health Excellent 5

struct Animal. Type typedef char String 20 [ 21 ] ; enum Health. Type { Poor, Fair, Good, Excellent } ; struct Animal. Type { long id ; String 20 name ; String 20 genus ; String 20 species ; String 20 country ; int age ; float weight ; Health. Type health ; }; Animal. Type // declares a struct data type // does not allocate memory struct members this. Animal ; // declare variables of Animal. Type 6 another. Animal ;

struct type declaration SYNTAX struct Type. Name { Member. List }; Member. List // does not allocate memory SYNTAX Data. Type Member. Name ; . . . 7

struct type declaration The struct declaration names a type and names the members of the struct. It does not allocate memory for any variables of that type! You still need to declare your struct variables. 8

More about struct type declarations If the struct type declaration precedes all functions it will be visible throughout the rest of the file. If it is placed within a function, only that function can use it. It is common to place struct type declarations with Type. Names in a (. h) header file and #include that file. It is possible for members of different struct types to have the same identifiers. Also a non-struct variable may have the same identifier as a structure member. 9

Accessing struct members Dot ( period ) is the member selection operator. After the struct type declaration, the various members can be used in your program only when they are preceded by a struct variable name and a dot. EXAMPLES this. Animal. weight another. Animal. country 10

Valid operations on a struct member depend only on its type this. Animal. age = 18; this. Animal. id = 2037581; cin >> this. Animal. weight; cin. get ( this. Animal. species, 21 ); strcpy ( this. Animal. name, “giant panda” ); this. Animal. genus[ 0 ] = toupper (this. Animal. genus[ 0 ] ) ; this. Animal. age++; if ( strcmp ( this. Animal. country, “Ceylon” ) == 0 ) strcpy ( this. Animal. country, “Sri Lanka” ); 11

Aggregate struct operations l I/O and comparisons of entire struct variables are NOT ALLOWED! l Operations valid on an entire struct type variable: assignment to another struct variable of same type, pass to a function as parameter (by value or by reference), return as value of a function. 12

Examples of aggregate struct operations another. Animal = this. Animal ; // assignment Write. Out(this. Animal); // value parameter Change. Weight. And. Age(this. Animal); // reference parameter this. Animal = Get. Animal. Data( ); // return value of function NOW WE’LL WRITE THE 3 FUNCTIONS USED HERE. . . 13

void Write. Out( /* in */ Animal. Type this. Animal) // Prints out values of all members of this. Animal // Precondition: // Postcondition: all members of this. Animal are assigned all members have been written out { cout << “ID # “ << this. Animal. id << this. Animal. name << endl ; cout << this. Animal. genus << this. Animal. species << endl ; cout << this. Animal. country << endl ; cout << this. Animal. age << “ years “ << endl ; cout << this. Animal. weight << “ lbs. “ << endl ; cout << “General health : “ ; Write. Word ( this. Animal. health ) ; } 14

void Change. Weight. And. Age( /* inout */ Animal. Type& this. Animal) // Accepts weight from keyboard and adds 1 to age // Precondition: this. Animal. age is assigned // Postcondition: this. Animal. age == this. Animal. age at entry + 1 // && this. Animal. weight == value entered at keyboard { String 20 weight. Str ; double value ; char response ; this. Animal. age++ ; do { cout << “Enter weight for ID# “ << this. Animal. id << “ : “ ; cin. get ( weight. Str, 21 ) ; cin. ignore (80, ‘n’ ) ; // consume newline value = atof (weight. Str) ; // convert string to double cout << “You entered: “ << value << endl ; cout << “Is this correct (Y/N) ? “ << endl ; cin >> response ; response = toupper (response) ; } while ( response != ‘Y’ ) ; this. Animal. weight = float (value ) ; } 15

Animal. Type Get. Animal. Data ( void ) // Obtains all information about an animal from keyboard // Precondition: None // Postcondition: // Function value == Animal. Type members entered at kbd { Animal. Type this. Animal ; char response ; do { // have user enter all members until they are correct. . . } while (response != ‘Y’ ) ; return this. Animal ; } 16

Array of structures const int MAX_SIZE = 500 ; enum Health. Type { Poor, Fair, Good, Excellent } ; struct Animal. Type { long id ; String 20 name ; String 20 genus ; String 20 species ; String 20 country ; int age ; float weight ; Health. Type health ; }; Animal. Type bronx. Zoo [ MAX_SIZE ] ; // declares struct data type // 8 struct members // declares array 17

Animal. Type bronx. Zoo[MAX_SIZE] ; bronx. Zoo [0] [1] . . . bronx. Zoo [ 0 ]. id 3456219 bronx. Zoo [ 0 ]. name “camel” bronx. Zoo [ 0 ]. genus “Camelus” bronx. Zoo [ 0 ]. species “dromedarius” bronx. Zoo [ 0 ]. country “India” bronx. Zoo [ 0 ]. age 10 bronx. Zoo [ 0 ]. weight 992. 8 bronx. Zoo [ 0 ]. health Fair [ 498 ] [ 499 ] 18

Animal. Type bronx. Zoo[MAX_SIZE] ; . id . name . genus . species . country. age. weight. health bronx. Zoo [ 0 ] 3456219 “camel” “Camelus”“dromedarius” “India” 10 992. 8 Fair bronx. Zoo [ 1 ] bronx. Zoo [ 2 ] bronx. Zoo [ 3 ]. . . bronx. Zoo[498] bronx. Zoo[499] 19

Add 1 to the age member of each element of the bronx. Zoo array for ( j = 0 ; j < MAX_SIZE ; j++ ) bronx. Zoo[ j ]. age = bronx. Zoo[ j ]. age + 1 ; OR, for ( j = 0 ; j < MAX_SIZE ; j++ ) bronx. Zoo[ j ]. age++ ; 20

Write id and genus for each element of bronx. Zoo array from country “China” for ( j = 0 ; j < MAX_SIZE ; j++ ) if ( strcmp (bronx. Zoo[ j ]. country , “China” ) == 0 ) cout << bronx. Zoo[ j ]. id << bronx. Zoo[ j ]. genus << endl ; 21

Find total weight of all elements of the bronx. Zoo array float total = 0. 0 ; for ( j = 0 ; j < MAX_SIZE ; j++ ) total += bronx. Zoo[ j ]. weight ; 22

Hierarchical structures The type of a struct member can be another struct type. This is called nested or hierarchical structures. Hierarchical structures are very useful when there is much detailed information in each record. FOR EXAMPLE. . . 23

struct Machine. Rec Information about each machine in a shop contains: an id. Number, a written description, the purchase date, the cost, and a history (including failure rate, number of days down, and date of last service). 24

struct Date. Type { int month ; int day ; int year ; }; // Assume 1. . 12 // Assume 1. . 31 // Assume 1900. . 2050 struct Statistics. Type { float fail. Rate ; Date. Type last. Serviced ; int down. Days ; }; // Date. Type is a struct type struct Machine. Rec { int id. Number ; String 50 description ; Statistics. Type history ; Date. Type purchase. Date ; float cost ; }; // Statistics. Type is a struct type Machine. Rec machine ; inventory [ NUM_MACHINES ] ; 25 // array of struct type

struct type variable machine 7000 5719 “DRILLING…” . 02 1 25 1996 4 3 21 1995 8000. 0 . month. day. year. failrate . last. Serviced . id. Number. description. history . downdays. month. day. year . purchase. Date . cost machine. history. last. Serviced. year has value 1996 26

Unions in C++ DEFINITION A union is a struct that holds only one of its members at a time during program execution. EXAMPLE union Weight. Type { long wt. In. Ounces ; int wt. In. Pounds; float wt. In. Tons; } ; only one at a time 27

Using Unions union Weight. Type { long wt. In. Ounces ; int wt. In. Pounds; float wt. In. Tons; } ; // declares a union type Weight. Type weight; // declares a union variable weight. wt. In. Tons = 4. 83 ; // Weight in tons is no longer needed. Reuse the memory space. weight. wt. In. Pounds = 35; 28