Structures

Union

• An union is a user defined data type just like structure except that in union same memory space is used for all members of union.

Defining a Union

• A structure can be defined by using keyword union.
• The union statement defines a new data type.
• To define a union we have to specify all the members that we want to group together along with their datatypes.

union unionName  
{
    datatype member1 ;
    datatype member2 ;
    ----------------
};  

        union student
        {
            int rollno;
            char name[20];
            int age;
            char gender;
        };

Design a union employee containing members empno , name , job and salary.

  union employee
  {
    int empno;
    char name[20];
    char job[20];
    int salary ;
  };

Design a union book containing members book_title , Author , price and total_pages.

  union book
  {
    char book_title[10];
    char author[10];
    int price;
    int total_pages;
  };

union Variables

• While defining union we can specify list of variables after ending brace.
Syntax:

  union unionName  
  {
    datatype member1;
    datatype member2;
    ----------------- 
  } variablesList ;

For eg:

        union student
        {
            int rollno;
            char name[20];
            int age;
            char gender;
        }

• After defining union, variables can be defined in local or global declaration by using syntax
Syntax:
union unionName variablelist;
For eg:
union student a,b,c;

Accessing union Members

• Whenever a union variable is created space is reserved for all its members.
• To access any member of a union, we use the member access operator (.)

  #include<stdio.h>
  union student
  {
	int rollno;
	char name[20];
	int age;
	char gender;
  };
  main()
  {
    union student a;
    printf("Enter RollNo Name Age and Gender : ");
    scanf("%d %s %d %c",&a.rollno,a.name,&a.age,&a.gender);
	
    printf("\nRollNo is %d",a.rollno);
    printf("\nName is %s",a.name);
    printf("\nAge is %d",a.age);
    printf("\nGender is %c",a.gender);
  }

Enter RollNo Name Age and Gender : 1333 Amit 21 M
RollNo is 1333
Name is Amit
Age is 21
Gender is M
  

  #include<stdio.h>
  union person
  {
    char fname[20];
    char lname[20];
    int age;
  };
  main()
  {
    union person a;
    printf("Enter fname lname and age: ");
    scanf("%s %s %d", a.fname, a.lname, &a.age);
    if(a.age>=60)
        printf("%s %s is Senior Citizen", a.fname, a.lname);
    else
        printf("%s %s is NOT Senior Citizen", a.fname, a.lname);
  }

Enter fname lname and age: Amit Jain 21
Amit Jain is NOT Senior Citizen