Visual C++ assert- String subscript out of range

My program is a solution for the Day 6 question in Advent of Code 2015. I get an error when I use "Start Without Debugging" and enter the puzzle input in the output window.The image contains the exact error I received. The error is related to "string subscript out of range". I would like help in resolving this error.

const int r = 1000;//global variable
const int c = 1000;//global variable
int lights[r][c];//global array

void instruction(string inp)//extracting OFF, ON, or toggle indication from the instruction
{
    int* loc;
    int coord[4] = { 0 };
    char cond = inp[7];
    loc = &coord[3];

    switch (cond)
    {
    case 'f':
        coordinates(loc, inp);
        execute(coord, cond);
        break;
    case 'n':
        coordinates(loc, inp);
        execute(coord, cond);
        break;
    default:
        coordinates(loc, inp);
        execute(coord, cond);
        break;
    }
}

void coordinates(int* loc, string inp)//extracting coordinates from the instruction
{
    int i, k = 0, l;
    l = inp.length()-1;
    for (i = l; inp[i] != ','; i--)
    {
        *loc += (inp[i]-'0') * pow(10,k);
        k++;
    }
    i--;
    loc--;
    k = 0;
    for (; inp[i] != ' '; i--)
    {
        *loc += (inp[i]-'0') * pow(10,k);
        k++;
    }
    i = i - 9;
    loc--;
    k = 0;
    for (; inp[i] != ','; i--)
    {
        *loc += (inp[i]-'0') * pow(10,k);
        k++;
    }
    i--;
    loc--;
    k = 0;
    for (; inp[i] != ' '; i--)
    {
        *loc += (inp[i]-'0') * pow(10,k);
        k++;
    }
}

void execute(int coord[], char cond)
{
    int i, j;
    for (i = coord[0]; i <= coord[2]; i++)
    {
        for (j = coord[1]; j <= coord[3]; j++)
        {
            if (cond == 'f')
                lights[i][j] &= 0;
            else if (cond == 'n')
                lights[i][j] |= 1;
            else
                lights[i][j] = ~lights[i][j];
        }
    }
}

int main()
{
    int i, j, k, count = 0;
    string inp;

    for (i = 0;;i++)
    {
        cout << "Enter an instruction" << endl;
        cin >> inp;

        if (inp != "xx")//To manually move to counting the number of lights turned ON
            instruction(inp);
        else
        {
            for (j = 0; j < r class="hljs-keyword">for (k = 0; k < c class="hljs-keyword">if (lights[j][k])
                        count++;
                }
            }
            cout << endl << "Number of lights lit " << count class="hljs-keyword">break;
        }
    }
    return 0;
}