PAT 1084 Broken Keyboard

#include <cstdio>
#include <cstdlib>
#include <vector>

using namespace std;

char linea[82];
char lineb[82];
bool tbl[256];

char cap(char ch) {
     if (ch >= 'a' && ch <= 'z') {
        ch -= 'a' - 'A';
     }
     return ch;
}

int main() {
    scanf("%s", linea);
    scanf("%s", lineb);
    vector<char> broken;
    char cha, chb;
    int ia = 0, ib = 0;
    while (linea[ia]!= '' && lineb[ib] != '') {
          cha = cap(linea[ia]);
          chb = cap(lineb[ib]);
          if (cha == chb) {
              ia++, ib++;              
          } else {
              if (!tbl[cha]) {
                 broken.push_back(cha);
                 tbl[cha] = true;
              }
              ia++;
          }
    }
    while (linea[ia] != '') {
        cha = cap(linea[ia]);
        if (!tbl[cha]) {
           broken.push_back(cha);
           tbl[cha] = true;
        }
        ia++;
    }
    int len = broken.size();
    for (int i=0; i<len; i++){
        printf("%c", broken[i]);    
    }
    system("pause");    
    return 0;    
}

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