Code works fine in CodeBlocks, but I get a RE when I upload it to Google Kickstart competition

Question

I'm trying to solve the first problem "Wiggle Walk" of Google KickStart Round C 2019. You can find more information here: https://codingcompetitions.withgoogle.com/kickstart/round/0000000000050ff2/0000000000150aac I've tried some test input and everything seems to work fine. However when I submit my attempt I get a Runtime Error. Any idea of why is this happening?

#include <iostream>
using namespace std;

int main() {
    int T, N, R, C, Sr, Sc;
    string str;
    cin >> T;
    for (int i = 1; i <= T; i++) {
        cin >> N >> R >> C >> Sr >> Sc;
        cin >> str;
        Sr -= 1;
        Sc -= 1;
        int a[R][C];
        for (int j = 1; j <= R; j++) {
            for (int k = 1; k <= C; k++) {
                a[j-1][k-1] = 0;
            }
        }
        a[Sr][Sc] = 1;
        for (int j = 1; j <= N; j++) {
            if (str.at(j-1) == 'E') {
                while (a[Sr][Sc+1] == 1) {
                    Sc += 1;
                }
                Sc += 1;
                a[Sr][Sc] = 1;
            }
            else if (str.at(j-1) == 'W') {
                while (a[Sr][Sc-1] == 1) {
                    Sc -= 1;
                }
                Sc -= 1;
                a[Sr][Sc] = 1;
            }
            else if (str.at(j-1) == 'S') {
                while (a[Sr+1][Sc] == 1) {
                    Sr += 1;
                }
                Sr += 1;
                a[Sr][Sc] = 1;
            }
            else if (str.at(j-1) == 'N') {
                while (a[Sr-1][Sc] == 1) {
                    Sr -= 1;
                }
                Sr -= 1;
                a[Sr][Sc] = 1;
            }
        }
        cout << "Case #" << i << ": " << Sr+1 << " " << Sc+1;
        if (i != T) {
            cout << "" << endl;
        }
    }
    return 0;
}

Answer 1

For those interested, I was able to solve both test sets with the following code:

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

int main() {
    int T, N, R, C, SR, SC;
    string str;
    cin >> T;
    for (int i = 1; i <= T; i++) {
        cin >> N >> R >> C >> SR >> SC;
        cin >> str;
        SR -= 1;
        SC -= 1;
        vector<vector<bool> > a(R, vector<bool>(C));
        a[SR][SC] = 1;
        for (int j = 1; j <= N; j++) {
            if (str.at(j-1) == 'E') {
                while (a[SR][SC+1] == 1) {
                    SC += 1;
                }
                SC += 1;
                a[SR][SC] = 1;
            }
            else if (str.at(j-1) == 'W') {
                while (a[SR][SC-1] == 1) {
                    SC -= 1;
                }
                SC -= 1;
                a[SR][SC] = 1;
            }
            else if (str.at(j-1) == 'S') {
                while (a[SR+1][SC] == 1) {
                    SR += 1;
                }
                SR += 1;
                a[SR][SC] = 1;
            }
            else if (str.at(j-1) == 'N') {
                while (a[SR-1][SC] == 1) {
                    SR -= 1;
                }
                SR -= 1;
                a[SR][SC] = 1;
            }
        }
        cout << "Case #" << i << ": " << SR+1 << " " << SC+1 << endl;
    }
    return 0;
}