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. Logic to get first set bit of a number using C program.

Input any number: 22

First set bit: 1

Required knowledge

Bitwise operators, Data types, Variables and Expressions, Basic input/output, If else, For 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 first bit of any odd number is always set.

Logic to get lowest order set bit

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

Step by step descriptive logic to get lowest order set bit.

1. Input number from user. Store it in some variable say, num.
2. Find total bits required to store an integer in memory say, INT_SIZE = sizeof(int) * 8.
   

   Read more – How to find size of a data type using sizeof() operator.

3. Run a loop from 0 to INT_SIZE. The loop structure should look like for(i=0; i<INT_SIZE; i++).
4. Initialize a variable to store lowest order set bit, say order = 0;.
5. Inside the loop if i^th bit is set then update order to i i.e. order = i; and terminate from loop.

Program to get lowest order set bit

/**
 * C program to get 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 number from user */
    printf("Enter any number: ");
    scanf("%d", &num);

    /* 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((num>>i) & 1)
        {
            order = i;

            /* Terminate the loop */
            break;
        }
    }

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

    return 0;
}

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

Happy coding 😉