杭电ACM怎么老是错？

  http://acm.hdu.edu.cn/showproblem.php?pid=2034

#include <iostream>using namespace std;int main(){int a[101]={0},b[101]={0},c[101]={0},n,m;while(cin >> n >> m && (n != 0 && m != 0)){int i,j,k = 0;for(i = 0; i < n; i++)cin >> a[i];for(i = 0; i < m; i++)cin >> b[i];for(i = 0; i < n; i++){int f2 = 0;for(j = 0; j < m; j++){if(a[i] == b[j]){f2 = 1;break;}}if(f2 == 0){c[k++] = a[i];}}if(k == 0){cout << "NULL" << endl;continue;}c[k] = '\0';/*for(i = 0; i < k; i++)cout << c[i];*/for(i = 0; i < k; i++){int t = 0;bool flag = false;for(j = 0; j < k - i - 1; j++){if(c[j] > c[j+1]){t = c[j];    c[j] = c[j+1];          c[j+1] = t;          flag = true;}}if(flag)break;}for(j = 0; j < k; j++){cout << c[j];if(j + 1 == k)cout << endl;elsecout << " ";}}return 0;}