Count Set Bits in an Integer (C Program)

January 03, 2026

C Program to Check Prime Number Using Efficient Logic

Introduction A prime number is a number that has exactly two distinct positive divisors: 1 and itself. In this program, we check whether a given number is prime or not using a simple and efficient logic. This type of program is commonly used in mathematics, competitive programming, and basic algorithm learning for beginners in C programming. Problem Statement The task is to write a C program that determines whether a given integer is a prime number or not. The program takes a single integer input from the user and analyzes its divisibility. If the number has no divisors other than 1 and itself, it should be identified as a prime number; otherwise, it is not prime. This problem is important in number theory and has practical relevance in areas such as cryptography, data validation, and algorithm design. Algorithm / Logic Explanation To check whether a number is prime, we need to verify that it is not divisible by any number other than 1 and itself. The algorithm follows a si...

🔢 Count Set Bits in an Integer (C Program)

#include<stdio.h> int count_set_bits(int num) { unsigned int mask = (unsigned int)num; int count = 0; while(mask) { count += mask & 1; mask >>= 1; } return count; } int main( ) { int number; // printf("Enter the number: "); scanf("%d", &number); int result = count_set_bits(number); printf("The count of set bits is %d\\n", result); }

📘 Explanation:

This program counts the number of set bits (1s) in the binary representation of an integer using bitwise operations.

🔹 `mask & 1` checks the least significant bit (LSB) of the number.
🔹 If it's 1, `count` is incremented.
🔹 The mask is then right-shifted using `mask >>= 1` to check the next bit.
🔹 The loop continues until the entire binary number is processed.

🔸 Note: Casting `num` to `unsigned int` ensures correct behavior for negative numbers (avoiding sign extension).

🔍 Sample Output:

Input:
13

Output:
The count of set bits is 3

🏷️ Keywords:

count set bits C, number of 1s in binary, bitwise AND, C bit manipulation, right shift, count bits using loop

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C Program to Check Prime Number Using Efficient Logic