Lecture 10: Structures

Outline Introduction Structure Definitions and declarations Initializing Structures Operations on Structures members Structures as Functions Parameters Arrays of structures and Structures of array

Introduction Structures Collections 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 characterisctics in an object E.g Object Characteristics Book price, number of pages, year published Car price, year, model, colour Student name, matric_no, semester

Structure Definition Syntax struct StructureTypeName { structure member declaration list };  E.g. struct book { float price; int numpages; int year; };

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

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 A concluding semicolon E.g. struct book book1;

How does it look like in my program? #include struct book { float price; int numpages; int year; }; int main( ) { struct book book1; …… } #include struct book { float price; int numpages; int year; } book1; int main( ) { …… } or

Initializing structures e.g. struct book book1={ 25.50, 690, 2005 }; OR book1.price = 25.50; book1.numpages=690; book1.year = 2005;

Operations on structure members OperationNormal variableStructure member Read from user scanf( “ %f ”, &price);scanf( “ %f ”, &book1.price); Assign valueprice = 25.50;book1.price = 25.50; Print as output printf( “ %f\n ”, price);printf( “ %f\n ”, book1.price); Copy to a variable newprice = price;newprice=book1.price; Pass value to a function if(fun1(price) > 5)if(fun1(book1.price) > 5)

Multiple structure variables struct book my_book, his_book, her_book; my_book  price  numpages  year  price  numpages  year  price  numpages  year his_book her_book

Multiple structure 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”);

Sample program #include 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(“\n Enter number of pages : "); scanf("%d", &her_book.numpages); printf(“\n Enter year published : "); scanf("%d", &her_book.year); printf(“\n 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; }

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.

Structures as function parameters …… float compute_price(struct book bk); //function prototype … int main( ) {struct book bookC; …………… new_price = compute_price(bookC);//function call …… } float compute_price(struct book bkC) {……. bkC.price=bkC.price + tax; …… return(bkC.price); }

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. int main( ) {………. struct book b; b = read( ); ………. } struct book read( )//function definition {struct book bk; printf(“Enter price:”); scanf(“%f”, &bk.price); ….. return(bk); }

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=calc_year(aa, bb, bkC.year);//function call ……. }

Arrays of Structure 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];

How it looks like

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; }

How to access?? Suppose that for a given month, the monthly bonuses are already stored in each employee’s record, and we want to calculate the total amount to be received by each employee monthly. The following loop computes and prints the employee’s total amount for the month: double total_monthly_paid; for(counter = 0; counter < 50; counter++) { printf(“%s %s”, employees[counter].firstName, employees[counter].lastName); total_monthly_paid = employees[counter].monthlySalary + employees[counter].monthlyBonus; }

Structures as function parameters It is 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); ……. }

Sample program #include struct book { float price; int numpages; int year; }; 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; } struct book read() { struct book her_book; printf("Enter book price : "); scanf("%f", &her_book.price); printf(“\n Enter number of pages : "); scanf("%d", &her_book.numpages); printf(“\n Enter year published : \n"); 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"); }

Arrays in Structs Example const arraySize = 5; struct listType { int listElem[arraySize]; //array containing the list int listLength; //length of the list }; struct listType list;

How it looks like struct listType listElem listLength

Structs within a struct struct date { int day; int month; int year; }; struct student { int id_no; char name[20]; char address[20]; char combination[3]; int age; structure date def; structure date doa; }oldstudent, newstudent;

Structs within a struct struct salary { char name[20]; char department[10]; int basic_pay; int transport_allowance; int rental_allowance; int entertainment _allowance ; } employee; struct salary { char name [20]; char department[10]; int basic_pay; struct { int transport_allowance; int rental_allowance; int entertainment _allowance; } allowance; } employee;

Structs within a struct : How to access?? The salary structure contains a member named allowance which itself is a structure with 3 members. The members contained in the inner, structure namely transport, rental, and entertainment can be referred to as : employee allowance. transport employee. allowance. rental employee. allowance. entertainment

Structs within a struct : How to access?? An inner-most member in a nested structure can be accessed by chaining all the concerned. Structure variables (from outer-most to inner-most) with the member using dot operator. The following being invalid: employee. allowance // actual member is missing employee. rental // inner structure variable is missing

End of Lecture 10 – Q & A