Skip to main content

Union in C programming

By

         Unions are similar to structure. Its syntax and use is similar to structure. It also contains members whose individual data types may differ from one another. The distinction is that all members within union share the same storage area of computer memory, whereas each member within a structure is assigned its own unique storage. Thus, unions are used to conserve memory. Since same memory is shared by all members, one variable can reside into memory at a time. When another variable is set into memory, the previous is replaced i.e. previous can not persist. Thus, unions are useful for applications involving multiple members where values need to be assigned to all of the members at any one time. Therefore, although a union may contain many members of different types, it can handle only one member at a time.
             The compiler allocates a piece of storage that is large enough to hold the largest variable type in the union. For example
         The union is created as
                     union student
                               {
                                 int roll;
                                 float marks;
                              } ;

Here, the union student has members roll and marks. The data type of roll is integer which contains 2 bytes in memory and the data type of marks is float which contains 4 bytes in memory. As all union members share same memory, the compiler allocates larger memory (i.e. 4 bytes in this case).
         The declaration of union and its variable is similar to that of structure. The union variable can be passed to function and it can be member of any other structure. The union can be illustrated as following examples;
Example:
             Create an union named student that has roll and marks as member. Assign some values to these members one at a time and display the result one at a time.
 void main()
  {
   union student
            {   int roll;
                float marks;
             };
 union student st;
  st.roll=455;
 printf("\nRoll=%d",st.roll);
 st.marks=78;
 printf("\nMarks=\t%f",st.marks);
   }
output:
Roll=455
Marks=  78.000000

            If two members are used simultaneously, the output is unexpected as following
void main()
  {
   union student
        {     int roll;
             float marks;
         };
 union student st;
  st.roll=455;
  st.marks=78;
printf("\nRoll=%d",st.roll);
printf("\nMarks=\t%f",st.marks);
   }
output:
Roll=0

Marks=  78.000000
Labels:

Comments

Post a Comment

Popular posts from this blog

Recursive Function in C programming

By
             If a statement within the body of a function calls the same function, the function is called recursive function. Actually, recursion is a process by which a function calls itself repeatedly until some specified condition has been satisfied. This process is used for repetitive computations in which each action is stated in term of previous result. Many iterative or repetitive problems can be written in this form.                To solve a problem using recursive method, two conditions must be satisfied. They are: 1)       Problem could be written or defined in term of its previous result. 2)       Problem statement must include a stopping condition. /*   An example of recursive function to calculate factorial of a number.*/    #include<stdio.h>    #include<conio.h...
Post a Comment
Read more

Difference between Binary mode and Text Mode in C programming

By
There are mainly three difference between binary and text mode. They are as follow.               i.       In text mode, a special character EOF whose ASCII value is 26 is inserted after the last character in the file to mark the end of file. But, there is no such special character present in the binary mode. The binary mode files keep track of the end of file from the number of characters present in the directory entry of the file.             ii.       In text mode of file, text and numbers are stored as one character per byte. For example, the number 1234 occupies two bytes in memory but it occupies 4 bytes (one byte per character) in the file. But, in binary mode, the number occupies the number of bytes as it occupies in the memory. Thus,  the above number occupies two bytes in file also in the case o...
Post a Comment
Read more

Passing arrays to functions in C programming

By
Like any other variables, we can also pass entire array to a function. An array name can be named as an argument for the prototype declaration and in function header. When we call the function no need to subscript or square brackets. When we pass array that pass as a call by reference because the array name is address for that array. /* Program to illustrate passing array to function */ #include<stdio.h> void display(int) ; /* function prototype */ main( ) { int num[5] = {100, 20, 40, 15, 33, i ; clrscr( ) ; printf (“\n The content of array is \n”) ; for (i=0; i<5; i++) display (num[i]) ; /*Pass array element fo fun */ getch{ } ; } void display(int n) { printf (“\t%d”, n ) ; } Output:     The content of array is 100      20       40       15 3 /* Program to read 10 numbers from keyboard to store these num into array and then c...
Post a Comment
Read more