C# IndexOutOfRange Array Exception

Question

I'm trying to create a 2D char array to hold a grid of chars which will be used as a sort of 'map' for a 2D console game.

I am getting a:

IndexOutOfRange exception

..and cannot see why. I've stepped through the code in debug mode and still cannot see the issue.

It steps through the code fine until it hits X = 25 and Y = 1, the upper right boundary of my grid.

I have _gameWidth and _gameHeight created as follows, outside of main but still inside the class:

static int _gameWidth = 25;
static int _gameHeight = 15;

Following is the code that fails, when trying to generate and populate the grid. It fails at this point:

else if (x == _gameWidth && y == 1)
    _grid[x, y] = '╕';



static void GenerateGrid()
{
    for (int y = 1; y <= _gameHeight; y++)
    {
        for (int x = 1; x <= _gameWidth; x++)
        {
            if (x == 1 && y == 1)
                _grid[x, y] = '╒';
            else if (x == _gameWidth && y == _gameHeight)
                _grid[x, y] = '╛';
            else if (x == _gameWidth && y == 1)
                _grid[x, y] = '╕';
            else if (x == 1 && y == _gameHeight)
                _grid[x, y] = '╘';
            else if ((x != 1 && y == _gameHeight) || (x != _gameWidth && y == 1))
                _grid[x, y] = '═';
            else if ((x == 1 && y > 1 && y < _gameHeight) || (x == _gameWidth && y > 1 && y < _gameHeight))
                _grid[x, y] = '│';
            else
                _grid[x, y] = 'x';

        }
        Console.WriteLine("");
    }
}

We're missing the declaration of grid[,]

Henk Holterman
– Henk Holterman

2015-09-26 11:51:29 +00:00
Commented Sep 26, 2015 at 11:51 — Henk Holterman
– Henk Holterman, Commented Sep 26, 2015 at 11:51
Problem solved. Thanks for fast replies.

Tinderlog
– Tinderlog

2015-09-26 12:03:47 +00:00
Commented Sep 26, 2015 at 12:03 — Tinderlog
– Tinderlog, Commented Sep 26, 2015 at 12:03

Sophie Coyne · Accepted Answer · 2015-09-26 11:50:38Z

5

Change

for (int i = 1; i <= gameHeight; i++)

to

for (int i = 0; i < gameHeight; i++)

and do the same for width.

EDIT: This is because array indexes start at the number 0 and end with the length of the array minus 1.

answered Sep 26, 2015 at 11:50

Sophie Coyne

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1 Comment

Sophie Coyne Over a year ago

I love that despite the other one being chosen as the correct answer, this answer has more votes :p

boot4life · Accepted Answer · 2015-09-26 11:51:10Z

3

This exception means that you have accessed an invalid index. From the way you have written the loop I can tell that you think that indexes go from 1 to the length of the array. Arrays are zero-based, though. Use the standard loop form:

for (int i = 0; i < length; i++)

Your loop starts at one. You can use the Visual Studio for loop template. Just type "for<tab><tab>".

Your program might benefit from the Code Review Stack Exchange site.

answered Sep 26, 2015 at 11:51

boot4life

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