Using Modulo instead of two loops-CodePudding

I'm new at programming in general and learning C# right now.

I just wrote a little programm where I have to step through an int[] in a specific pattern. The pattern is as follows:

Start at the last entry of the array (int i)
form the sum of i and (if avaible) the three entrys above (e.g. i = i-1 ... i = i-3)
Change i to i -= 4 (if avaible)
Repeat from step 2 until i = 0;

Therefore i wrote the following loop:

        for (int i = intArray.Length - 1; i >= 0; i -= 4)
        {
            for (int a = 1; a <= 3; a  )
            {
                if (i - a >= 0)
                {
                    intArray[i]  = intArray[i - a];
                    intArray[i - a] = 0;
                }
            }
        }

Now my new assignment is to change my code to only use 1 loop with the help of modulo-operations. I do understand what modulo does, but i can't figure out how to use it to get rid of the second loop.

Maybe somebody explain it to me? Thank you very much in advance.

CodePudding user response：

iterating the array reversely makes it a bit more complicated, but what you wanted to get rid of inner loop with modulo is probably this:

        var intArray = Enumerable.Range(1, 15).ToArray();

        for (int i = 1; i < intArray.Length - 1;  i   )
        {
            intArray[i - (i % 4)]  = intArray[i];
            intArray[i] = 0;
        }

CodePudding user response：

While iterating over the array, the idea would be to use the modulo 4 operation to calculate the next index to which you will add the current value.

This should work with any array lengths:

        for (int i = 0; i < intArray.Length; i  ){
            // we check how far away we are from next index which stores the sum
            var offset = (intArray.Length - 1 - i) % 4;
            if (offset == 0) continue;
            intArray[i offset]  = intArray[i];
            intArray[i] = 0;
        }