Simplify list.add of unknown amount of entries

Question

So I am currently working on a calculator.

One of the requirements is to store the history, which I currently do in a list.

While I have simplified alot of code I can't get my head around simplifying this

           if (amountNumbers == 2)
            {
                memory.Add(userNumbers[0].ToString() + " " + op + " " + userNumbers[1].ToString() + " = " + calculation.ToString());
                userNumbers.Clear();
            }
            if (amountNumbers == 3)
            {
                memory.Add(userNumbers[0].ToString() + " " + op + " " + userNumbers[1].ToString() + " " + op + " " + userNumbers[2].ToString() + " = " + calculation.ToString());
                userNumbers.Clear();
            }
            if (amountNumbers == 4)
            {
                memory.Add(userNumbers[0].ToString() + " " + op + " " + userNumbers[1].ToString() + " " + op + " " + userNumbers[2].ToString() + " " + op + " " + userNumbers[3].ToString() + " = " + calculation.ToString());
                userNumbers.Clear();
            }
            if (amountNumbers == 5)
            {
                memory.Add(userNumbers[0].ToString() + " " + op + " " + userNumbers[1].ToString() + " " + op + " " + userNumbers[2].ToString() + " " + op + " " + userNumbers[3].ToString() + " " + op + " " + userNumbers[4].ToString() + " = " + calculation.ToString());
                userNumbers.Clear();
            }

Any idea how I simplify this and make the adding dynamic depending on how many values the user has chosen? Preferably I want to store the whole string within one index since that is how the history is being displayed.

Answer 1

Easy, loop over userNumbers and build your string, then add it to memory once you're done. Like so:

// Ensure that we don't get an 'IndexOutOfBoundsException'
// By clamping  'amountNumbers' to the length if 'userNumbers' if it's larger
if (amountNumbers > userNumbers.Length)
    amountNumbers = userNumbers.Length;

// You could use a normal 'string' and '... += ...' but 'StringBuilder' is more efficient
var sb = new StringBuilder();
for (int i = 0; i < amountNumbers; i++)
    sb.Append($"{userNumbers[i].ToString()} ");

// Add the calculation, no space at the start required as the loop adds a trailing space
sb.Append($"= {calculation.ToString()}");

memory.Add(sb.ToString());

Answer 2

Use .Take(amountNumbers) to get at most amountNumbers of user numbers, . And String.Join to combine strings with some separator between each:

var users = userNumbers.Take(amountNumbers).Select(s => s.ToString());
var str = string.Join(" " + op + " ", users);
memory.Add(str + " = " + calculation.ToString());

If you need some special handling for cases, like if amountNumbers< userNumbers.Count or amountNumbers == 1 you need to add that separately. If you know that amountNumbers == userNumbers.Count , then the .Take(...) is not needed.

Answer 3

You can just Join userNumbers values with " " + op + " " separator, then concat calculation at end:

string lastExpression = string.Join(" " + op + " ", userNumbers) + // Join values
                        " = " + calculation.ToString(); // Concat calculation result
memory.Add(lastExpression);
userNumbers.Clear();

There is no matter which amount of values in userNumbers - they all will be joined with " " + op + " " between each other.

Shorter version with string interpolation:

memory.Add($"{string.Join($" {op} ", userNumbers)} = {calculation}");
userNumbers.Clear();

EDIT. This is very similar idea with @JonasH 's answer, just without converting userNumbers to a collection of strings. Join makes it implicitly at behind.