C program to count the number of bits set in an unsigned integer(shift operator)

bit_count_shift.c

/**
  * Shift operators shift the bits in an integer variable by a specified
  * number of positions. The << operator shifts bits to the left, and the >>
  * operator shifts bits to the right. The syntax for these binary operators
  * is x << n and x >> n
  * Each operator shifts the bits in x by n positions in the specified
  * direction. For a right shift, zeros are placed in the n high-order bits
  * of the variable; for a left shift, zeros are placed in the n low-order
  * bits of the variable.
  * Here are a few examples:
  * Binary 00001000(decimal 8) right-shifted by 2 gives 00000010(decimal 2).
  * Binary 00001000(decimal 8) left-shifted by 3 gives 01000000(decimal 64).
  *
  * One of the application of shift operation is to count the number of bits
  * set in an unsigned integer.
  * For example: f(0) = 0, f(1) = 1, f(2) = 1, f(3) = 2.
  *
  * More @ http://en.wikipedia.org/wiki/Bitwise_operation
  **/
  
#include<stdio.h>

int main()
{
  unsigned int i, b[32] = {0};
  int j = 31, count = 0;
  printf("\nEnter the unsigned integer:");
  scanf("%d", &i);

  while(i != 0)
  {
    // Bitwise AND operation b/w i & 0x00000001 is 1
    // if the last bit of i is 1 and 0 if the last
    // last bit is 0
    b[j] = i & 0x00000001; 
    // Increment count whenever the bit is 1    
    if(b[j] == 1)
      count++;
    j--;
    // Right shifting i by 1 to get the next bit
    i = i >> 1;
  }

  printf("\nThe number of bits set in %d is %d", i, count);

  // The array b gives the binary representation of i
  printf("\nThe binary representation of %d is ", i);
  for(i = j + 1; j < 32; j++)
    printf("%d", b[j]); 

  return 0;
}