Decimal to binary

#include <stdio.h>

int main()
{
    int a;
    int *nr;
    int i, j;
    int s[100];
    printf("nr=");
    scanf("%d",&nr);
    printf("\n Ati introdus nr=%d",nr);
    a=nr;
    
    i=0;
    while(a>0)
    {s[i]=a%2;
     a=a/2;
     i++;
    }
    printf("\n Reprezentarea in binar este: ");
    for (j=i-1;j>=0;j--)
    {
        printf("%d",s[j]);
    }
    
    return 0;
}