Loop a loop inside a loop by simplifying

Question

I've been trying to simplify the following by putting it into a loop..

int A0 = 0, A1 = 0, A2 = 0;

for (A0 = 0; A0 < nums.Length; A0++)
{
    for (A1 = 0; A1 < nums.Length; A1++)
    {
        for (A2 = 0; A2 < nums.Length; A2++)
        {
            string ss = nums[A0] + nums[A1] + nums[A2];
            dataGridView1.Rows.Add(new string[] { ss });
        }
    }
}

like A0, A1 and A2, i need to go until A75. I can get the result if i nest like the above. But how can i put it on a loop..??

I tried this one:

int[] A = new int[3];

for (int i = 0; i < A.Length; i++)
{
    for (A[i] = 0; A[i] < nums.Length; A[i]++)
    {
        string ss = "";
        for (int j = 0; j < A.Length; j++) ss += nums[A[i]];
        dataGridView1.Rows.Add(new string[] { ss });
    }
}

But it will perform only like..

int A0 = 0, A1 = 0, A2 = 0;
for (A0 = 0; A0 < nums.Length; A0++)
{
    string ss = nums[A0] + nums[A1] + nums[A2];
    dataGridView1.Rows.Add(new string[] { ss });
}
for (A1 = 0; A1 < nums.Length; A1++)
{
    string ss = nums[A0] + nums[A1] + nums[A2];
    dataGridView1.Rows.Add(new string[] { ss });
}
for (A2 = 0; A2 < nums.Length; A2++)
{
    string ss = nums[A0] + nums[A1] + nums[A2];
    dataGridView1.Rows.Add(new string[] { ss });
}

Answer 1

An equivalent to

public void DoNestedThings()
{
    for(var A0 = 0; A0 < _max; A0 ++)
    {
        //...
        for(var i5 = 0; i5 < _max; i5++)
        {
            DoThing(new List<int>{i0, ..., i5});
        }
    }
}

Would be:

private void DoNestedThings(int depth, Stack<int> indexes)
{
    if(depth == 0)
    {
        DoThing(indexes);
        return;
    }
    for(var i = 0; i < _max; i++)
    {
        indexes.Push(i);
        DoNestedThings(depth-1, indexes);
        indexes.Pop();
    }
}

public void DoNestedThings()
{
    DoNestedThings(5, new Stack<int>());
}

This replaces nested loops with a single loop, but then uses recursion to enter into that loop multiple times. Each time the DoNestedThings method is called with depth > 0, you enter into another loop.

(Note the order of the indexes passed to DoThing will be reversed)