Question

I’m trying to generate prime numbers based on user input. This is what I have so far but I just can’t seem to figure it out:

Console.Write("Please enter the number of prime numbers you would like to see:");
int numberOfPrimes = Convert.ToInt32(Console.ReadLine());

for (int x = 0; x < numberOfPrimes; x++)
{
    for (int a = 2; a <= x ; ++a)
    {
        bool prime = true;
        for (int b = 2; b < a; ++b)
        {
            if (a % b == 0)
            {
                prime = false;
            }//end if
        }//end double nested for
        if (prime == true)
        {
            Console.WriteLine(a);
        }//end if
    }//end nested for
}//end for

Answer 1

You should be able to see why your results are wrong quite easily if you look at your loop structures. Step through them by hand (it won’t take long).

The reason that you are getting your current results is that not every iteration of the outer loop (x < numberOfPrimes) produces a result – it will skip quite a few iterations due to the way the inner loop is structured.

What you really need to do is restructure the inner loops. Your innermost loop works fine, and should detect any prime numbers. Your second loop, however, should only test numbers that haven’t yet been tested. Also, it should stop looping once you find a prime number.