Nested FOR loops: readability & performance [closed]

Question

I understand nested FOR loops. I understand what they do, and how they do it. But my problem is that they seem horribly unreadable to me.

Take this example:

for (int i = 0, y = 0; y <= ySize; y++) {
    for (int x = 0; x <= xSize; x++, i++) {
        vertices[i] = new Vector3(x, y);
    }
}

Now, this loop is pretty straightforward. It's just an x/y "2 dimensional" loop. But as I add more and more "dimensions" to this nested loop, is there a way to make the code not a horrible mess of nests within nests and stupid amounts of backtracing counter variables (i, x, y, z, etc.)?

Also, does additional nesting affect performance in a linear way, or do additonal FORs make things more and more inefficient as you nest more of them?

Answer 1

I think that the issue you have here is less the nested for loops, and more an unusual use of variables within the loops.

Newlines before the opening braces can help with readability too (although this is subjective).

How about this instead:

int i = 0;

for (int y = 0; y <= ySize; y++)
{
    for (int x = 0; x <= xSize; x++)
    {
        vertices[i++] = new Vector3(x, y);
    }
}

This approach should remain relatively readable for additional dimensions too (in this example I've moved the incrementing of i out to its own line, as suggested by usr).

int i = 0;

for (int y = 0; y <= ySize; y++)
{
    for (int x = 0; x <= xSize; x++)
    {
        for (int a = 0; a <= aSize; a++)
        {
            for (int b = 0; b <= bSize; b++)
            {
                vertices[i] = new Vector3(x, y, a, b);

                i++;
            }
        }
    }
}

Regarding performance, I would suggest focussing on making sure that the code is readable and understandable by a human first, and then measuring the run-time performance, possibly with a tool such as RedGate ANTS

Answer 2

The usual solution is to refactor into methods which contain one or two for loops, and keep refactoring until each method is clear and not too large.

Another solution to stop the indenting, and to separate the loop-resulting-data from the applying-logic, is to use Linq.

int i = 0;
var coordinates = from y in Enumerable.Range(0, ySize + 1)
                  from x in Enumerable.Range(0, xSize + 1)
                  select new { x, y, i = i++ };

foreach (var coordinate in coordinates) {
    vertices[coordinate.i] = new Vector3(coordinate.x, coordinate.y);
}

This is only if the vertices array is already declared. If you can just create a new array, then you can do simply this:

var vertices = (from y in Enumerable.Range(0, ySize + 1)
                from x in Enumerable.Range(0, xSize + 1)
                select new Vector3(coordinate.x, coordinate.y)
               ).ToArray();