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

3 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 Example: Object Characteristics Book price, number of pages, year published Car price, year, model, colour Student name, matric_no, semester

4 Syntax: struct StructureTypeName { structure member declaration list }; Example: struct book { float fPrice; int iNumPages; int iYear; };

5 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

6 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;

7 #include struct book { float fPrice; int iNumPages; int iYear; }; int main( ) { struct book sBook1; …… } #include struct book { float fPrice; int iNumPages; int iYear; } sBook1; int main( ) { …… } or struct book sBook1;

8 struct book sBook1 = {25.50, 690, 2005}; OR sBook1.fPrice = 25.50; sBook1.iNumPages = 690; sBook1.iYear = 2005; dot operator

9 OperationNormal variableStructure member Read from user scanf(“%f”, &fPrice); scanf(“%f”, &sBook1.fPrice); Assign value fPrice = 25.50;sBook1.fPrice = 25.50; Print as output printf(“%f\n”, fPrice);printf(“%f\n”, sBook1.fPrice); Copy to a variable fNewPrice = fPrice;fNewPrice = sBook1.fPrice; Pass value to a function if(fnFun1(fPrice) > 5)if(fnFun1(sBook1.fPrice) > 5)

10 struct book sMyBook, sHisBook, sHerBook; sMyBook  fPrice  iNumPages  iYear  fPrice  iNumPages  iYear  fPrice  iNumPages  iYear sHisBook sHerBook

11 Example: int main() { … 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”); … }

12 #include 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; }

13 #include 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; } Enter book price : Enter number of pages : 450 Enter year published : 2012 My book : Her book : My book is the latest publication.

14  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.

15 …… 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); }

16 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); }

17 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 …… }

18 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); …… }

19 #include 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"); }

20 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];

21 [0] [1] [2]... [25] [26]... [48] [49] Array of structs asEmployees asEmployees[2] acFirstName acLastName iPersonID acDeptID dYearlySalary dMonthlySalary dYearToDatePaid dMonthlyBonus

22 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; }

23 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 paycheck for(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; }

24 Example : const arraySize = 5; struct listType { int aiListElem[arraySize]; //array containing the list int iListLength; //length of the list }; struct listType sList;

25 struct listType aiListElem iListLength

26 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; }; struct contactType { string acPhone; string acCellphone; string acFax; string acPager; string ac ; }; struct employeeType { struct nameType sName; string acEmplID; struct addressType sAddress; struct dateType sHiredate; struct dateType sQuitdate; struct contactType sContact; string acDeptID; double dSalary; };

27 //variable declaration struct employeeType sNewEmployee; //declare 100 employees' records struct employeeType asEmployees[100]; sNewEmployee.dSalary = ; sNewEmployee.sName.acFirst = "Mary"; sNewEmployee.sName.acMiddle = "Beth"; sNewEmployee.sName.acLast = "Simmons";

28 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

29 Q & A!