Structure

What is Structure?

Structure is one of the important data type in C language. Structure is a programmers-defined data type in C language. Structure allows us to combine dissimilar data types to a single variable.

Syntax of Structure

A structure variable in C can be declared using “struct” keyword. The general form of structure is as under:

struct s_name {

            data_type1 var_1;

            data_type1 var_2;

            ….

            Data_typen var_n;

}struct_var1, struct_var2;

• struct is keyword of C language.

• Structure name is s_name

•  var_1 is one of the variable of structure s_name with data type data_type1(which may be any valid C language data type like int, float, char, etc.)

• struct_var1, struct_var2 are the variables of structure s_name;

Example of Structure declaration

struct student{

char name[20];

int rollno;

float percentage;

}s1, s2;

Difference between Array and Structure

• Array is a collection of variables of same datatype

• Structure is a collection of variables with different datatypes

• Array uses index or subscript for accessing array elements

• Structures uses (.) operator for accessing structure members

• Array is a derived data type where as structure is defined by programmers

Examples of Structure

• Array of Structure

• Dynamic Memory Allocation for Structure

• Accessing structure members using pointers

• Writing Structure to data file

• Reading Structure from file
• Writing a student data into a file using a structure
• Nested Structure (Person Structure into Student) 

Sample Structure Program

C program to show use of Structure concept. //C program to demonstrate use of Structure in Library System. #include <stdio.h> #include <string.h> struct Book{    int   book_id;    char  book_title[30];    char  book_publisher[30];    char  book_subject[30]; }; void main( ) {    struct Book myBook;  // Declare variable of type Book    //Initialise values to myBook variable    myBook.book_id=101;       printf("Enter Book Title:");    gets(myBook.book_title);       printf("Enter Book Publisher Name:");    gets(myBook.book_publisher);       printf("Enter Book Subject:");    gets(myBook.book_subject);       /* print myBook details */    printf( "Book ID: %d\n", myBook.book_id);    printf( "Book Title: %s\n", myBook.book_title);    printf( "Book Publisher Name : %s\n", myBook.book_publisher);    printf( "Book Subject : %s\n", myBook.book_subject); } //Output Enter Book Title:Computer Studies Enter Book Publisher Name:ABC India Enter Book Subject:Computer Science Book ID: 101 Book Title: Computer Studies Book Publisher Name : ABC India Book Subject : Computer Science