Solution of LIGHT OJ 1214 :: Large Division

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/**Bismillahir Rahmanir Rahimm**/

#include <stdio.h>
int main()
{
    long long int tst, i, j, b, dcml;
    char a[1000];
    scanf("%lld", &tst);
    for(i=1; i<=tst; i++)
    {
        long long int mod_a=0, div_a=0;
        scanf("%s", a);
        scanf("%lld", &b);
        j=0;
        if(a[0]=='-') j=1;
        while(a[j])
        {
            dcml = a[j] - 48;
            div_a+=dcml;
            mod_a = div_a%b;
            div_a= mod_a*10;
            j++;
        }
        if(mod_a==0) printf("Case %lld: divisible\n", i);
        else printf("Case %lld: not divisible\n", i);
    }
    return 0;
}