Getting exit status -1 when filling a dynamic array

Question

For some reason, even though I've looked and made myself as sure as I can be I'm doing this right, I keep getting exit status -1 in this code. I'm simply trying to create a dynamic 2d array and to fill each value with a 0:

Grid::Grid(int _rows, int _cols){

    Grid::rows = _rows;
    Grid::cols = _cols;

    Grid::grid = new int*[Grid::rows];

    for(int i = 0; i < Grid::rows; i++){

        Grid::grid[i] = new int[Grid::cols];

    }

    for(int i = 0; i < 1; i++){

        for(int j = 0; j < 1; i++){

            Grid::grid[i][j] = 0;

        }

    }
}

I've done some testing and the code runs fine without the second for loop when I'm trying to fill the array, so I think the problem is there, even though I can't see what would be wrong with it.

Here's the class just in case:

class Grid{

    private:

    int rows;
    int cols;
    int** grid;

    public:

    Grid(int _rows, int _cols);
    int getRows(){return rows;}
    int getCols(){return cols;}
    int** getGrid(){return grid;}
    void deleteArray();

};

I'm new to c++, so go easy on me if it's an obvious mistake. Thanks for the help.

Welcome on stackoverflow. Please read this: [ask] and [edit] your question and post a [mcve]. — Jabberwocky, Feb 28 '19 at 06:55
do you have to use a dynamic arrays with new and so on, or are you willing or able to use a `std::vector`?? — skratchi.at, Feb 28 '19 at 07:08
`for(int i = 0; i < 1; i++)` -- Why are you looping just one time? — PaulMcKenzie, Feb 28 '19 at 07:10

score 1 · Accepted Answer · answered Feb 28 '19 at 07:13

I'm afraid you haven't looked very hard

for(int i = 0; i < 1; i++){

    for(int j = 0; j < 1; i++){

        Grid::grid[i][j] = 0;

    }

}

should be

for (int i = 0; i < rows; i++) {
    for (int j = 0; j < cols; j++) {
        grid[i][j] = 0;
    }
}

You were incrementing the wrong variable in your inner loop (which meant it would have looped for ever). And for some reason you had a limit of 1 on your loops instead of rows and cols.

And there is no need to prefix your member variables with Grid::.

score 0 · Answer 2 · answered Feb 28 '19 at 07:10

Congrats, your code works fine. The only problem is you have made a typo.

for(int i = 0; i < 1; i++){

    for(int j = 0; j < 1; j++){ //previously was i++

        Grid::grid[i][j] = 0;

    }

}

Also, you have used static limit "1". which can throw an error if rows/cols are less than 1.

skratchi.at · Answer 3 · 2019-02-28T07:58:43.383

Your specific problem is simple to solve. You increment the wrong variable in the inner for-loop

for(int i = 0; i < Grid::rows; i++){ // loop over all elements

    for(int j = 0; j < Grid::cols; j++){ // j++ NOT i++ // also loop over all elements

        Grid::grid[i][j] = 0;

    }

}

My advice here is to use longer variable names, which differ more.

for(int idx_row = 0; idx_row < Grid::rows; ++idx_row){

    for(int idx_col = 0; idx_col < Grid::cols; idx_col++){

        Grid::grid[idx_row][idx_col] = 0;

    }

}

Getting exit status -1 when filling a dynamic array

3 Answers3