Check prime numbers in an interval or range [N...M]. From Fundamentals of Computer Programming with C# http://www.introprogramming.info/wp-content/uploads/2013/07/Books/CSharpEn/Fundamentals-of-Computer-Programming-with-CSharp-Nakov-eBook-v2013.pdf
Console.Write("n = ");
int n = int.Parse(Console.ReadLine());
Console.Write("m = ");
int m = int.Parse(Console.ReadLine());
for (int num = n; num <= m; num++)
{
bool prime = true;
int divider = 2;
int maxDivider = (int) Math.Sqrt(num);
while (divider <= maxDivider)
{
if (num % divider == 0)
{
prime = false;
break;
}
divider++;
}
if (prime)
{
Console.Write(" " + num);
}
}
// n = 3
// m = 9
// 3 5 7