This C Program converts a decimal number into binary & count the number of 1s. 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.
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)
{
no_of_1s++;
}
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);
}

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