Prime factor within a range of numbers

Question

I tried running this code in visual studio. It doesn't output anything and runs infinite loop.

    private void calculateButton_Click(object sender, EventArgs e)
        {
            int startNumber, endNumber, counter, num;
            startNumber = Convert.ToInt32(minValue.Text);
            endNumber = Convert.ToInt32(maxValue.Text);
            int startNumCounter = startNumber;
            for (num = startNumCounter; num <= endNumber; num++)
            {
                counter = 0;

                int numCurrent = num;
                for (int i = 2; i <= num; i++)
                {
                    if (numCurrent % i == 0)
                    {
                        output.Text += " " + i + " ";
                        num = num / i;
                        counter++;


                    }


                    if (counter != 0 && num >= 2)
                        output.Text = "Factors: " + num;
                }

            }

        }
    }
}

Expected output: Min 7, Max: 10 ...... 8: 2 * 2 * 2. 9: 3 * 3. 10: 2 * 5. So it finds prime factors of numbers within min and max range. If the numbers inside the range are primes it doesn't count prime factor for.

Answer 1

This is the code I came up with:

private void calculateButton_Click(object sender, EventArgs e)
        {
            int startNumber, endNumber, counter, num;
            startNumber = Convert.ToInt32(minValue.Text);
            endNumber = Convert.ToInt32(maxValue.Text);
            int startNumCounter = startNumber;
            for (num = startNumCounter; num <= endNumber; num++)
            {
                output.Text += $"Factors {num}:";
                counter = 0;
                int numCurrent = num;

                for (int i = 2; i <= numCurrent; i++)
                {
                    bool continueToNexti = false;
                    while (!continueToNexti)
                    {
                        if (numCurrent % i == 0)
                        {
                            output.Text += $" {i} ";
                            numCurrent = numCurrent / i;
                            counter++;
                        }
                        else
                        {
                            continueToNexti = true;
                        }
                    }

                }
                output.Text += Environment.NewLine;
            }
        }

Some notes on this: The reason your code didn't end is that this line

num = num / i;

which should have been

numCurrent = numCurrent / i;

Furthermore I came up with an extra loop, the While loop, to account for the fact that a number may be dividable by the same factor multiple times.

And to speed things up a bit, I changed

for (int i = 2; i <= num; i++)

to

for (int i = 2; i <= numCurrent; i++)