C :

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>
int a[10001];
int main(){
    int n,i,k=0;
    scanf("%d",&n);
    if(n==0){
    	printf("%d",0);
    	return 0;
	}
    while(n!=0){
    	k++;
    	a[k] = n%2;
    	n = n/2;
	}
	for(i=k;i>=1;i--){
		printf("%d",a[i]);
	}
    return 0;
}

Python :

n = int( input() )
s=''
while n==0:
    print('0')
    break
while n!=0:
    s = str(n % 2) + s
    n = n // 2
print(s)