Difference between Structure and Union in C

Structure

structure is a user-defined data type

It is the collection of different data elements

struct keyword is used to define a structure

dot operator(.) is used for accessing members.

when a variable is associated with a structure, the  compiler allocates the  memory for each member. 

The size of structure is greater than or equal to the sum of sizes of its members.

Individual member can be accessed at a time.

Syntax:

struct[structure name]

{

Member definition;

Member definition;

..

Member definition

};

Example:

struct Employee

{

    char name[50]; //1byte memory

    int id;                //2 byte

    float salary;        //4byte   

} e1;

Note

7 bytes memory is allocated because the compiler allocates the memory for each member.

#include <stdio.h>

#include<conio.h>

struct Employee

{

    char name[50];

    int id;

    float salary;

} e1;

void main()

{

    clrscr();

    printf("Enter  Employee information:\n");

    printf("Enter NAME: ");

    scanf("%s", e1.name);

    printf("Enter ID: ");

    scanf("%d", &e1.id);

    printf("Enter SALARY: ");

    scanf("%f", &e1.salary);

    printf("Employee Information:\n");

    printf("Name: %s\n",e1.name);

    printf("Id: %d\n",e1.id);

    printf("Salary: %f\n", e1.salary);

   getch();

}

Output:

Enter  Employee information:                                                                                                   

Enter NAME: surya                                                                                                              

Enter ID: 123                                                                                                                  

Enter SALARY: 35000                                                                                                            

Employee Information:                                                                                                          

Name: surya

Id: 123                                                                                                                        

Salary: 35000.000000 

 Union

 union is a user-defined data type

It is the collection of different data elements

union keyword is used to define a structure

dot operator(.) is used for accessing members.

when a variable is associated with a union, the  compiler allocates the  memory by considering the size of the   largest memory. So size of union is equal to the size of largest member

only one member can be accessed at a time.    

Syntax:

union[union name]

{

Member definition;

Member definition;

..

Member definition

};

Example:

union Employee

{

    char name[50]; //1byte memory

    int id;                //2 byte

    float salary;        //4byte   

} e1;

Note

4 bytes memory is allocated because the compiler allocates the memory by considering the size of the   largest memory

#include <stdio.h>

#include<conio.h>

union Employee

{

    char name[50];

    int id;

    float salary;

} e1;

void main()

{

    clrscr();

    printf("Enter  Employee information:\n");

    printf("Enter NAME: ");

    scanf("%s", e1.name);

    printf("Enter ID: ");

    scanf("%d", &e1.id);

    printf("Enter SALARY: ");

    scanf("%f", &e1.salary);

    printf("Employee Information:\n");

    printf("Name: %s\n",e1.name);

    printf("Id: %d\n",e1.id);

    printf("Salary: %f\n", e1.salary);

   getch();

}

 Output:

Enter Employee information:                                                                                                   

Enter NAME: surya                                                                                                              

Enter ID: 101                                                                                                                  

Enter SALARY: 12456                                                                                                            

Employee Information:                                                                                                          

Name:

Id: 1178771456                                                                                                                 

Salary: 12456.000000  

Note

Only salary is displayed here because the compiler allocates the  memory by considering the size of the   largest memory(salary is the largest size )