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 the lowest order set bit of the given number using bitwise operator. How to find first set bit in a given number using bitwise operator in C programming. Finding first set bit in a binary number using C program.

Example

Input

Input any number: 22

Output

First set bit: 1

Required knowledge

Basic C programming, Bitwise operator, If else, Loop

Lowest order set bit

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 the first bit of any odd number is always set.
Lowest order set bit

Program to get lowest order set bit

/**
 * C program to find lowest order set bit in a number
 */

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

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

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

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

    //Loops over each bit of the integer
    for(i=0; i<INT_SIZE; i++)
    {
        //If the current bit is set
        if((num>>i) & 1)
        {
            order = i;
            break; //No need to check further
        }
    }

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

    return 0;
}

Note: Here I have assumed that bit ordering starts from 0.

Output

Enter any number: 22
Lowest order set bit in 22 is 1

Happy coding 😉

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