How do I find the biggest prime number between 1 to maxvalue

Question

I'm having hard time coding a program to find prime number between 1to maxvalue in c#

it keeps on displaying some random numbers that never ends.

int num;
int k;

for (int i=int.MaxValue; i>0; i--)
{
    for(num=i-1; num>0; num--)
    {
        if(i != num &&  i % num !=0)
        {
            k = num;
            break;
        }
        else
        {
            continue;
        }

    }
    Console.Write(k);
}

Answer 1

Try this code:

int maxValue = 30;
bool isPrime;
for (int i = maxValue; i > 1; i--)
{
    isPrime = true;
    for (int j = 2; j <= Math.Floor(Math.Sqrt(i)); j++)
        if(i % j == 0)
        {
            isPrime = false;
            break;
        }

    if (isPrime)
        MessageBox.Show(i.ToString());
}