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.

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


As I explained in how to find highest order set bit finding lowest order set bit is also very easy if you know how to check if a bit is set or not. What you need to do is to iterate over each bit of the number and stop when you find the first 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;

    //Reads 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.

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

Happy coding ;)

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