How Do I calcualte a for loop to display in a listbox where the first loop is user input but the remaining iterations are calculated? : I am trying to create a loop that will calculate inside a listbox but run the actual calculation after the first statement and compound the remaining...

Here is my code:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-html -->

     // Count Loop   
                    int numdays;
                    numdays = 1;

                    // Declare and Assign Variables
                    double organism, daysmultiply, dailyincrease;
                    organism = double.Parse(OrganismTextBox.Text);
                    dailyincrease = double.Parse(DailyIncreaseTextBox.Text);
                    daysmultiply = double.Parse(DaysMultiplyTextBox.Text);
                    ResultsListBox.Items.Clear();

                    // Need to have daily increase texbox formatted as a percentage - unsure how

                    for (numdays = 0;  numdays <= daysmultiply; numdays++)
                    {
                        ResultsListBox.Items.Add(" Day " + numdays + " Popualtion is " + (organism * dailyincrease));
                        numdays = numdays++;

<!-- end snippet -->




The result of the calculation is a loop that calculates .6 each time it iterates. I am trying to figure out how to compound the loop each time.
Can someone please help?