Lecture 12 - Structures

Transcription

1 Lecture 12 - Structures 1

2 Outline Introduction Structure Definitions and Declarations Initializing Structures Operations on Structures Members Structures as Functions Parameters Array of Structures 2

3 Introduction Structures Collection of related data items called components (or members) that are NOT necessarily of the same data type. Commonly used to define records to be stored in files. Usually the collections of related data item are characteristics in an object For example: Object Book Car Student Characteristics price, number of pages, year published price, year, model, colour name, matrix no, semester 3

4 Structure Definition Syntax: struct StructureTypeName structure member declaration list ; Example: struct book float price; int numpages; int year; ; 4

5 Structure Definition struct information A struct cannot contain an instance of itself Can contain a member that is a pointer to the same structure type A structure definition does not reserve space in memory Instead creates a new data type used to define structure variables 5

6 Structure Declaration After defining a structure type, we may declare variables that are of that type. A structure variable declaration requires these elements : keyword struct structure type name a list of variables names separated by commas concluding semicolon E.g. struct book book1; struct book my_book,his_book,her_book; 6

7 How does it look like in my program? #include <stdio.h> struct book float price; int numpages; int year; ; int main( ) struct book book1; OR #include <stdio.h> struct book float price; int numpages; int year; book1; int main( ) struct book book1; 7

8 Initializing Structures struct book book1 = 25.50, 690, 2005; OR book1.price = 25.50; book1.numpages = 690; book1.year = 2005; dot operator 8

9 Operations on Structures Members Operation Normal variable Structure member Read from user scanf( %f, &price); scanf( %f, &book1.price); Assign value price = 25.50; book1.price = 25.50; Print as output printf( %f\n, price); printf( %f\n, book1.price); Copy to a variable Pass value to a function newprice = price; newprice = book1.price; if(fun1(price) > 5) if(fun1(book1.price) > 5) 9

10 Multiple Structures Variables struct book my_book, his_book, her_book; price numpages year price numpages year price numpages year my_book his_book her_book 10

11 Multiple Structures Variables e.g. struct book my_book, his_book, her_book; my_book.price = 25.50; her_book.price = 10.50; if(my_book.price > her_book.price) printf( My book is more expensive than hers\n ); else printf( My book is cheaper than hers\n ); 11

12 Sample Program #include <stdio.h> struct book float price; int numpages; int year; ; int main() struct book my_book = 25.50,690,2005; struct book her_book; printf("enter book price : "); scanf("%f", &her_book.price); printf("enter number of pages : "); scanf("%d", &her_book.numpages); printf("enter year published : "); scanf("%d", &her_book.year); printf("my book :\n"); printf("%.2f\t%d\t%d\n", my_book.price, my_book.numpages, my_book.year); printf("her book :\n"); printf("%.2f\t%d\t%d\n", her_book.price, her_book.numpages, her_book.year); if(my_book.year > her_book.year) printf("my book is the latest publication\n"); else printf("her book is the latest publication\n"); return 0; 12

13 Structures as Function Parameters Like variables of any other data type, structure variables can be used as formal and actual function parameters. In passing structure variables by value to a function, the operating systems makes a copy of the entire structure in the data area of the called function. 13

14 Structures as Function Parameters float compute_price(struct book bk); int main() struct book bookc; new_price = compute_price(bookc); return 0; float compute_price(struct book bkc) bkc.price=bkc.price + tax; return(bkc.price); //function prototype //function call //function definition 14

15 Structures as Function Parameters A nonvoid function of a structure type can return a structure of that structure type under the function s name if we use a return statement in the function. struct book read (); int main( ). struct book b; b = read( );. //function prototype //function call struct book read () //function definition struct book bk; printf( Enter price: ); scanf( %f, &bk.price);.. return(bk); 15

16 Structures as Function Parameters If all members of a structure variable are not needed for a function to perform its task, we can pass only the required members. However, we must specify structure members using the component selection operator. int modify_year(int a, int b, int year); //function prototype int main ( ) struct book bkc; avg_year=modify_year(aa, bb, bkc.year); //function call. 16

17 Structures as Function Parameters It is also possible to pass structure variables using pointers. int main() struct book b; read(&b); //function call void read(struct book *bk) printf( Enter price: ); scanf( %f, &bk->price); printf( Enter numpages: ); scanf( %d, &bk->numpages);. 17

18 struct book read() struct book her_book; #include <stdio.h> struct book float price; int numpages; int year; ; Sample Program struct book read(); void print(struct book, struct book); void compare(int, int); int main() struct book my_book = 25.50,690,2005; struct book she_book; she_book=read(); print(my_book, she_book); compare(my_book.year, she_book.year); return 0; printf("enter book price : "); scanf("%f", &her_book.price); printf("enter number of pages : "); scanf("%d", &her_book.numpages); printf("enter year published : "); scanf("%d", &her_book.year); return(her_book); void print(struct book my_book, struct book her_book) printf("my book :\n"); printf("%.2f\t%d\t%d\n", my_book.price, my_book.numpages, my_book.year); printf("her book :\n"); printf("%.2f\t%d\t%d\n", her_book.price, her_book.numpages, her_book.year); void compare(int my_year, int she_year) if(my_year > she_year) printf("my book is the latest publication\n"); else printf("her book is the latest publication\n"); 18

19 An Array of Structures Suppose a company has 50 full-time employees. struct employeetype char firstname[20]; char lastname[20]; int personid; char deptid[10]; double yearlysalary; double monthlysalary double yeartodatepaid; double monthlybonus; ; struct employeetype employees[50]; - to declare for 100 employees' records: struct employeetype employees[100]; 19

20 How it looks like 20

21 How to access?? int counter; for(counter = 0; counter < 50; counter++) scanf( %s %s %d %s %lf, &employees[counter].firstname, &employees[counter].lastname, &employees[counter].personid, &employees[counter].deptid, &employees[counter].yearlysalary); employees[counter].monthlysalary = employees[counter].yearlysalary/12; employees[counter].yeartodatepaid = 0.0; employees[counter].monthlybonus = 0.0; 21

22 How to access?? Suppose that for a given month the monthly bonuses are already stored in each employee s record, and we have to calculate the monthly paycheck and update the yeartodatepaid amount. The following loop computes and prints the employee s paycheck for the month: double paycheck; //variable to calculate the paycheck for(counter = 0; counter < 50; counter++) printf( %s %s, employees[counter].firstname, employees[counter].lastname); paycheck = employees[counter].monthlysalary + employees[counter].monthlybonus; employees[counter].yeartodatepaid = employees[counter].yeartodatepaid + paycheck; 22

23 Arrays in Structures Example const arraysize = 5; struct listtype int listelem[arraysize]; int listlength; ; //array containing the list //length of the list struct listtype list; 23

24 How it looks like struct listtype listelem listlength 24

25 Structure Within a Structure struct nametype string first; string middle; string last; ; struct addresstype string address1; string address2; string city; string state; string zip; ; struct datetype string month; string day; string year; ; struct contacttype string phone; string cellphone; string fax; string pager; string ; ; struct employeetype struct nametype name; string emplid; struct addresstype address; struct datetype hiredate; struct datetype quitdate; struct contacttype contact; string deptid; double salary; ; 25

26 Structure within a Structure: How to access?? //variable declaration struct employeetype newemployee; Example: newemployee.salary = ; newemployee.name.first = "Mary"; newemployee.name.middle = "Beth"; newemployee.name.last = "Simmons"; 26

27 Structure Within a Structure : How to access?? The statement scanf( %s, &newemployee.name.first); reads and stores a string into newemployee.name.first. The statement newemployee.salary = newemployee.salary * 1.05; updates the salary of newemployee 27