PAT basic 1029

#include <iostream>#include <cctype>using namespace std;int main() {    string a, b;    cin >> a >> b;    char c[80];    int flag, index = 0;    for (int i = 0; i < a.length(); i++) {        flag = 0;        for (int j = 0; j < b.length(); j++) {            if (a[i] == b[j]) {                flag = 1;                break;            }        }        if (!flag) c[index++] = toupper(a[i]);    }    for (int i = 1; i < index; i++) {   //去掉重复的字符         for (int j = 0; j < i; j++) {            if (c[i] == c[j]) {                c[i] = '#';                break;            }        }    }    for (int i = 0; i < index; i++)        if (c[i] != '#') cout << c[i];    return 0;}