I checked my program, and I'm pretty sure that it gives the correct answers for the sample input/output, and for all the tests given on this forum. I also went to the page of NEERC 2002 and downloaded their test examples, and everything seems to be correct.

I tried ending output with or without a newline('\n'), and I still can't figure out why I could possibly be getting a wrong answer three times in a row.

Please give me some advice as to where my problem is. Maybe it is someting small? Maybe I misread something in the problem statement?

Anyway, here's my program(I'm sure the code is pretty bad, but keep in mind that I don't have much experience with these sorts of problems):

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    int A[10002];
    long int pos = 0;

    cin.unsetf(ios::skipws);

    do {
        char input[3];

        cin >> input[0];

        if(input[0] == '\n') break;

        cin >> input[1];

        input[2] = 0;

        A[pos] = (int) strtol(input, (char **) input + 2 * sizeof(char), 16);
        pos++;

    } while(1);

    int current;
    int key;

    char input[3];
    input[0] = 'C';
    input[1] = '9';
    input[2] = 0;

    cin >> input[0] >> input[1];
    key = (int) strtol(input, (char **) input + 2 * sizeof(char), 16);
    key ^= 32;

    for(int i = 0; i < pos; i++) {
            cout << hex << uppercase << setfill('0') << setw(2) << key;

            cin >> input[0] >> input[1];

            current = (int) strtol(input, (char **) input + 2 * sizeof(char), 16);

            key = ((key) ^ (A[i])) ^ (current);
    }

    cout << hex << uppercase << setfill('0') << setw(2) << key << "\n";

    return 0;
}

Please help! Any advice will be appreciated!