本地跑一点问题没有 交上去就是0分WA

#include <cstdio>
using namespace std;
int n, x, m;
void output(int num)
{
    if(num == 0)
        return;
    output(num / m);
    int b = num % m;
    putchar(b < 10 ? '0' + b : 'A' - 10 + b);
    return;
}
int main()
{
    scanf("%d", &n);
    getchar();
    char c = '0';
    while(c != '\n')
    {
        x = x * n + (c >= '0' && c <= '9' ? c - '0' : c - 'A' + 10);
        c = getchar();
    }
    scanf("%d", &m);
    output(x);
    putchar('\n');
    return 0;
}