进制转换问题，请问我为啥只有90分？

#include<bits/stdc++.h>
using namespace std;
char a[16] = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
char ans[1001];
int main(){
	long long m, x;
	cin >> x >> m;
	long long i = 0;
	while(x != 0){
		int t = x%m;
		x = x/m;
		ans[i++] = a[t];
	}
	for(int j = i-1; j >= 0; j--){
		cout << ans[j];
	}
	return 0;
}