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C program to get lowest order or first set bit of a number



C program to get lowest order or first set bit of a number

Write a C program to input any number from user and find lowest order set bit of given number using bitwise operator. How to find first set bit in a given number using bitwise operator in C programming.

Lowest order or first set bit of any number is the first bit set starting from left to right. Lowest order set bit of any odd number is 0 since first bit of any odd number is always set.

Logic to get lowest order set bit is almost similar to highest order set bit of a number.

Input number from user. Store it in some variable say, j.
Find total bits required to store an integer in memory say, INT_SIZE = sizeof(int) * 8.
Run a loop from 0 to INT_SIZE. The loop structure should look like for(i=0; i<INT_SIZE; i++).
Initialize a variable to store lowest order set bit, say order = 0;.
Inside the loop if ith bit is set then update order to i i.e. order = i; and terminate from loop.

#include <stdio.h>
#define INT_SIZE sizeof(int) * 8 /* Integer size in bits */

int main()
{
    int j, order, i;

    /* Input number from user */
    printf("Enter any number: ");
    scanf("%d", &j);

    /* Initially set the order to max size of integer */
    order = INT_SIZE - 1;

    /* Iterate through each bit of integer */
    for(i=0; i<INT_SIZE; i++)
    {
        /* If current bit is set */
        if((j>>i) & 1)
        {
            order = i;

            /* Terminate the loop */
            break;
        }
    }

    printf("Lowest order set bit in %d is %d", j, order);

    return 0;
}