C # recursive function not all code paths return value

Question

I try to make a recursive function, but I get this error: not all code paths return a value . I know why I get this error because if does not return something, but I do not want to return something ... How to get around this error? (This should be just a warning)

  private double calculate(double money, int months) { months--; if (months != 0) calculate(profit * 0.3, months); else return profit; } 

Edit: I call it that when the user clicks a button

  private void bCalculate_Click(object sender, EventArgs e) { profit = double.Parse(tbMoney.Text); months = int.Parse(tbMonth.Text); tbPpofit.Text = calculate(profit,months+1).ToString(); } 

If I write return, as you say, it will not give the result that I need

Answer 1

Just add the return to the recursive branch:

  if (months != 0) return calculate(profit * 0.3, months); ... 

Answer 2

Add a return value to the recursion code:

  if (months != 0) return calculate(profit * 0.3, months);