C Program to Convert Decimal to Binary and Count the Number of 1s


This is a C Program to convert a decimal number to binary & count the number of 1s.

Problem Description

This C Program converts a decimal number into binary & count the number of 1s.

Problem Solution

The program uses module operation and multiplication with base 2 operation for conversion. It also uses modulo operation to check for 1’s and accordingly increments the count of 1s.

Program/Source Code

Here is source code of the C program to convert a decimal number to binary & count the number of 1s. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

 * C program to accept a decimal number and convert it to binary
 * and count the number of 1's in the binary number
#include <stdio.h>
void main()
    long num, decimal_num, remainder, base = 1, binary = 0, no_of_1s = 0;
    printf("Enter a decimal integer \n");
    scanf("%ld", &num);
    decimal_num = num;
    while (num > 0)
        remainder = num % 2;
        /*  To count no.of 1s */
        if (remainder == 1)
        binary = binary + remainder * base;
        num = num / 2;
        base = base * 10;
    printf("Input number is = %d\n", decimal_num);
    printf("Its binary equivalent is = %ld\n", binary);
    printf("No.of 1's in the binary number is = %d\n", no_of_1s);
Program Explanation

In this C program, we are reading the decimal number using ‘num’ variable. A decimal number system is a base 10 number system using digits for 0 to 9 whereas binary number system is base 2 and uses 0 and 1. Check whether the number is less than or equal to zero. Divide the number by 2 and store the remainder in the array. Increase the length of the array by 1. After the execution of while loop, print the binary number and the number of 1’s.

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Runtime Test Cases
$ cc pgm46.c
$ a.out
Enter a decimal integer
Input number is = 134
Its binary equivalent is = 10000110
No.of 1's in the binary number is = 3

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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