Structures in C: Usage and Examples

Arrays allow to define type of variables that can hold several data items of the same kind. Similarly structure is another user-defined data type available in C that allows combining data items of different kinds.

Structure helps to construct a complex data type in a more meaningful way. It is somewhat similar to an Array. The only difference is that array is used to store collection of similar datatypes while structure can store a collection of any type of data.

Structure is used to represent a record. Suppose you want to store record of Student which consists of student name, address, roll number and age. You can define a structure to hold this information.

Structure Definition in C

struct keyword is used to define a structure. struct defines a new data type which is a collection of different types of data.

struct structure_name
{
 //declaration of different data types
};

The closing braces in the structure type declaration must be followed by a semicolon(;).

Syntax of structure

struct structure_name 
{
    data_type member1;
    data_type member2;
    .
    .
    data_type memeber;
};

Note: Don't forget the semicolon }; in the ending line.

We can create the structure for a person as mentioned above as:

struct person
{
    char name[50];
    int citNo;
    float salary;
};

This declaration above creates the derived data type struct person.

Structure variable declaration

When a structure is defined, it creates a user-defined type but, no storage or memory is allocated.

Declaring Structure variables separately

For the above structure of a person, variable can be declared as:

struct person
{
    char name[50];
    int citNo;
    float salary;
};

int main()
{
    struct person person1, person2, person3[20];
    return 0;
}

Declaring Structure Variables with Structure definition

Another way of creating a structure variable is:

struct person
{
    char name[50];
    int citNo;
    float salary;
} person1, person2, person3[20];

In both cases, two variables person1, person2 and an array person3 having 20 elements of type struct person are created.

Accessing members of a structure

There are two types of operators used for accessing members of a structure.

1. Member operator(.)
2. Structure pointer operator(->)

Any member of a structure can be accessed as:

structure_variable_name.member_name

Suppose, we want to access salary for variable person2. Then, it can be accessed as:

person2.salary

Structure Initialization

Like any other data type, structure variable can also be initialized at compile time.

struct Patient
{
 float height;
 int weight;  
 int age; 
};

struct Patient p1 = { 180.75 , 73, 23 };    //initialization

or

struct patient p1;
p1.height = 180.75;     //initialization of each member separately
p1.weight = 73;
p1.age = 23;

Example Program

Program

#include <stdio.h>  
#include <string.h>  
struct employee    
{   int id;    
    char name[50];    
}e1;  //declaring e1 variable for structure  
int main( )  
{  
   //store first employee information  
   e1.id=101;  
   strcpy(e1.name, "Rambo Azmi");//copying string into char array  
   //printing first employee information  
   printf( "employee 1 id : %d\n", e1.id);  
   printf( "employee 1 name : %s\n", e1.name);  
   return 0;  
}  

Output

employee 1 id : 101
employee 1 name : Rambo Azmi
Press any key to continue . . .

Program

#include <stdio.h>
#include <string.h>
 
struct Books {
   char  title[50];
   char  author[50];
   char  subject[100];
   int   book_id;
};
 
int main( ) {

   struct Books Book1;        /* Declare Book1 of type Book */
   struct Books Book2;        /* Declare Book2 of type Book */
 
   /* book 1 specification */
   strcpy( Book1.title, "C Programming");
   strcpy( Book1.author, "Rambo Azmi"); 
   strcpy( Book1.subject, "C Programming Tutorial");
   Book1.book_id = 6495407;

   /* book 2 specification */
   strcpy( Book2.title, "Telecom Billing");
   strcpy( Book2.author, "Snowfish");
   strcpy( Book2.subject, "Telecom Billing Tutorial");
   Book2.book_id = 6495700;
 
   /* print Book1 info */
   printf( "Book 1 title : %s\n", Book1.title);
   printf( "Book 1 author : %s\n", Book1.author);
   printf( "Book 1 subject : %s\n", Book1.subject);
   printf( "Book 1 book_id : %d\n", Book1.book_id);

   /* print Book2 info */
   printf( "Book 2 title : %s\n", Book2.title);
   printf( "Book 2 author : %s\n", Book2.author);
   printf( "Book 2 subject : %s\n", Book2.subject);
   printf( "Book 2 book_id : %d\n", Book2.book_id);

   return 0;
} 

Output

Book 1 title : C Programming
Book 1 author : Rambo Azmi
Book 1 subject : C Programming Tutorial
Book 1 book_id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Snowfish
Book 2 subject : Telecom Billing Tutorial
Book 2 book_id : 6495700
Press any key to continue . . .