Structures

1. Structures EKT 120 Computer Programming

2. Outline • Introduction • Structure Definitions and Declarations • Initializing Structures • Operations on Structures Members • Structures as Functions Parameters • Array of Structures EKT 120 Computer Programming

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: ObjectCharacteristics Book price, number of pages, year published Car price, year, model, colour Student name, matric_no, semester EKT 120 Computer Programming

4. Structure Definition • Syntax: • struct StructureTypeName { structure member declaration list }; Example: struct book { float fPrice; int iNumPages; int iYear; }; EKT 120 Computer Programming

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 EKT 120 Computer Programming

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 sBook1; struct book sMyBook,sHisBook,sHerBook; EKT 120 Computer Programming

7. How does it look like in my program? #include <stdio.h> struct book { float fPrice; int iNumPages; int iYear; } sBook1; int main( ) { …… } #include <stdio.h> struct book { float fPrice; int iNumPages; int iYear; }; int main( ) { struct book sBook1; …… } or struct book sBook1; EKT 120 Computer Programming

8. Initializing Structures struct book sBook1 = {25.50, 690, 2005}; OR sBook1.fPrice = 25.50; sBook1.iNumPages = 690; sBook1.iYear = 2005; dot operator EKT 120 Computer Programming

9. Operations on Structures Members EKT 120 Computer Programming

10. Multiple Structures Variables struct book sMyBook, sHisBook, sHerBook; • fPrice • fPrice • fPrice • iNumPages • iNumPages • iNumPages • iYear • iYear • iYear sMyBook sHisBook sHerBook EKT 120 Computer Programming

11. Multiple Structures Variables e.g. struct book sMyBook, sHisBook, sHerBook; sMyBook. fPrice = 25.50; sHerBook.fPrice = 10.50; if(sMyBook.fPrice > sHerBook.fPrice) printf(“My book is more expensive than hers\n”); else printf(“My book is cheaper than hers\n”); EKT 120 Computer Programming

12. Sample Program #include <stdio.h> struct book { float fPrice; int iNumPages; int iYear; }; int main() { struct book sMyBook = {25.50,690,2005}; struct book sHerBook; printf("Enter book price : "); scanf("%f", &sHerBook.fPrice); printf("Enter number of pages : "); scanf("%d", &sHerBook.iNumPages); printf("Enter year published : "); scanf("%d", &sHerBook.iYear); printf("My book :\n"); printf("%.2f\t%d\t%d\n", sMyBook.fPrice, sMyBook.iNumPages, sMyBook.iYear); printf("Her book :\n"); printf("%.2f\t%d\t%d\n", sHerBook.fPrice, sHerBook.iNumPages, sHerBook.iYear); if(sMyBook.iYear > sHerBook.iYear) printf("My book is the latest publication\n"); else printf("Her book is the latest publication\n"); return 0; } EKT 120 Computer Programming

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. EKT 120 Computer Programming

14. Structures as Function Parameters …… float fnComputePrice(struct book sBkC);//function prototype … int main( ) { struct book sBookC; …………… fNewPrice = fnComputePrice(sBookC); //function call …… } float fnComputePrice(struct book sBkC) //function definition { ……. sBkC.fPrice=sBkC.fPrice + fTax; …… return(fBkC.fPrice); } EKT 120 Computer Programming

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 fnRead (); //function prototype int main( ) { ………. struct book sB; sB = fnRead( ); //function call ………. } struct book fnRead( ) //function definition { struct book sBk; printf(“Enter price:”); scanf(“%f”, &sBk.fPrice); ….. return(sBk); } EKT 120 Computer Programming

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 fnModifyYear(int iA, int iB, int iYear); //function prototype …….. int main( ) { struct book sBkC; ……………. iAvgYear=fnModifyYear(iAa, iBb, sBkC.iYear); //function call ……. } EKT 120 Computer Programming

17. Structures as Function Parameters • It is possible to pass structure variables using pointers int main() { struct book sB; ……… fnRead(&sB); //function call } void fnRead(struct book *sBk) { printf(“Enter price:”); scanf(“%f”, &sBk->fPrice); printf(“Enter numpages:”); scanf(“%d”, &sBk->iNumPages); ……. } EKT 120 Computer Programming

18. #include <stdio.h> struct book { float fPrice; int iNumPages; int iYear; }; struct book fnRead(); void fnPrint(struct book, struct book); void fnCompare(int, int); int main() { struct book sMyBook = {25.50,690,2005}; struct book sSheBook; sSheBook=fnRead(); fnPrint(sMyBook , sSheBook); fnCompare(sMyBook.iYear, sSheBook.iYear); return 0; } struct book fnRead() { struct book sHerBook; printf("Enter book price : "); scanf("%f", &sHerBook.fPrice); printf("Enter number of pages : "); scanf("%d", &sHerBook.iNumPages); printf("Enter year published : "); scanf("%d", &sHerBook.iYear); return(sHerBook); } void fnPrint(struct book sMyBook, struct book sHerBook) { printf("My book :\n"); printf("%.2f\t%d\t%d\n", sMyBook.fPrice, sMyBook.iNumPages, sMyBook.iYear); printf("Her book :\n"); printf("%.2f\t%d\t%d\n", sHerBook.fPrice, sHerBook.iNumPages, sHerBook.iYear); } void fnCompare(int iMyYear, int iSheYear) { if(iMyYear > iSheYear) printf("My book is the latest publication\n"); else printf("Her book is the latest publication\n"); } Sample Program EKT 120 Computer Programming

19. An Array of Structures • Suppose a company has 50 full-time employees. struct employeeType { char acFirstName[20]; char acLastName[20]; int iPersonID; char acDeptID[10]; double dYearlySalary; double dMonthlySalary; double dYearToDatePaid; double dMonthlyBonus; }; struct employeeType asEmployees[50]; EKT 120 Computer Programming

20. How it looks like Array of structs asEmployees EKT 120 Computer Programming

21. How to access?? int iCounter; for(iCounter = 0; iCounter < 50; iCounter++) { scanf(“%s %s %d %s %lf”, &asEmployees[iCounter].acFirstName, &asEmployees[iCounter].acLastName, &asEmployees[iCounter].iPersonID, &asEmployees[iCounter].acDeptID, &asEmployees[iCounter].dYearlySalary); asEmployees[iCounter].dMonthlySalary = asEmployees[iCounter].dYearlySalary/12; asEmployees[iCounter].dYearToDatePaid = 0.0; asEmployees[iCounter].dMonthlyBonus = 0.0; } EKT 120 Computer Programming

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 dPayCheck; //variable to calculate the paycheckfor(iCounter = 0; iCounter < 50; iCounter++) { printf(“%s %s”, asEmployees[iCounter].acFirstName, asEmployees[iCounter].acLastName); dPayCheck = asEmployees[iCounter].dMonthlySalary + asEmployees[iCounter].dMonthlyBonus; asEmployees[iCounter].dYearToDatePaid = asEmployees[iCounter].dYearToDatePaid + dPayCheck; } EKT 120 Computer Programming

23. Arrays in Structures • Example const arraySize = 5; struct listType { int aiListElem[arraySize]; //array containing the list int iListLength; //length of the list }; struct listType sList; EKT 120 Computer Programming

24. How it looks like • struct listType aiListElem iListLength EKT 120 Computer Programming

25. Structure Within a Structure struct contactType { string acPhone; string acCellphone; string acFax; string acPager; string acEmail; }; struct employeeType { struct nameType sName; string acEmplID; struct addressType sAddress; struct dateType sHiredate; struct dateType sQuitdate; struct contactType sContact; string acDeptID; double dSalary; }; struct nameType { string acFirst; string acMiddle; string acLast; }; struct addressType { string acAddress1; string acAddress2; string acCity; string acState; string acZip; }; struct dateType { string acMonth; string acDay; string acYear; }; EKT 120 Computer Programming

26. Structure Within a Structure : How to access?? //variable declaration struct employeeType sNewEmployee; //declare 100 employees' records struct employeeType asEmployees[100]; sNewEmployee.dSalary = 45678.00; sNewEmployee.sName.acFirst = "Mary"; sNewEmployee.sName.acMiddle = "Beth"; sNewEmployee.sName.acLast = "Simmons"; EKT 120 Computer Programming

27. Structure Within a Structure : How to access?? The statement scanf(“%s”, &sNewEmployee.sName.acFirst); reads and stores a string into sNewEmployee.sName.acFirst. The statement sNewEmployee.dSalary = sNewEmployee.dSalary * 1.05; updates the salary of newEmployee EKT 120 Computer Programming

28. TQ EKT 120 Computer Programming