This program is to set and clear a particular bit in a given number.

The logic used will be:

• To set a particular bit: ORing the bit with 1
• To clear the particular bit: ANDing the bit with 0.
• All the numbers are represented in 32 bits.

#include <stdio.h>
#define MAX_SIZE sizeof(int) *8

int display_binary (unsigned int num)
{
   int i;
   for(i = MAX_SIZE-1; i>=0; i--)
   {
       if((num >> i)&1)
         printf("1");
       else
         printf("0");
   }
}

int main()
{
  unsigned int num, pos;
  printf("\n Enter the number: ");
  scanf("%d", &num);
  printf("\n Enter the position: ");
  scanf("%d", &pos);

  /* To set the bit */
  printf("\n The org number is: %d   :", num);
  display_binary(num);

  num = num | (1UL << pos);
  printf("\n The new number after setting %d bit is: %u  binary:", pos, num);
  display_binary(num);
  
  /* To clear the bit */
  num = num & ~(1UL << pos);
  printf("\n The new number after clearing bit %d is: %u  binary:", pos, num);
  display_binary(num);
  return 0;
}

Output:

Enter the number: 12
Enter the position: 4

The org number is: 12   :00000000000000000000000000001100
The new number after setting 4 bit is: 28  binary:00000000000000000000000000011100
The new number after clearing bit 4 is: 12  binary:00000000000000000000000000001100

Example:
For simplicity it is shown in 8 bits.

To set:

num = 8 = 0000 1000
mask = 1 << 2 = 0000 0100

num | mask = 0000 1100 = 12

To clear:

num = 8 = 0000 1000
mask = 1 << 2 = 0000 0100
~mask = 1111 1011

num & ~maks = 0000 1000 = 8

Categories: C Language