Arsalan’s Musings

Problem: Given a range of integers, count the number of primes. Also list the prime numbers in the range.

using System;

namespace SolvingSmallProblems
{
    public class Program
    {
        static void Main(string[] args)
        {
            int defaultLowNum = 1;
            int defaultHighNum = 50;
            int lowNum, highNum;
            PrimeNumberPuzzles prime = new PrimeNumberPuzzles();

            Console.WriteLine("PRIME NUMBER COUNT PROGRAM");
            Console.WriteLine();
            Console.WriteLine("Please enter start number");
            try
            {
                lowNum =
                Convert.ToInt32(Console.ReadLine());
            }
            catch (Exception)
            {
                lowNum = defaultLowNum;
            }

            Console.WriteLine("Please enter end number");
            try
            {
                highNum = Convert.ToInt32(Console.ReadLine());
            }
            catch (Exception)
            {
                highNum = defaultHighNum;
            }

            if (lowNum < 1)
            {
                lowNum = defaultLowNum;
            }
            if (highNum < lowNum)
            {
                highNum = defaultHighNum;
            }

            int totalPrimes = prime.CountPrimes(lowNum, highNum);
            Console.WriteLine();
            Console.WriteLine("Total number of prime numers between " +
                lowNum.ToString() + " and " + highNum.ToString() +
                " is " + totalPrimes + ".");
            Console.ReadKey();
        }
    }

    public class PrimeNumberPuzzles
    {
        public int CountPrimes(int low, int high)
        {
            int count = 0;
            for (int num = low; num <= high; num++)
            {
                if (IsPrime(num))
                {
                    Console.Write(num + " ");
                    count++;
                }
            }
            return count;
        }

        bool IsPrime(int num)
        {
            bool isNumPrime = true;
            if ( num == 2)
            {
                return true;
            }
            else if (num == 1)
            {
                return false;
             }
            else if (num < 1)
            {
                throw new Exception("Invalid number!");
            }
            else
            {
                int remainder;
                for (int test = 2; test < num - 1; test++)
                {
                    remainder = num % test;
                    if (remainder == 0)
                    {
                        isNumPrime = false;
                    }
                }
                return isNumPrime;
            }
        }
    }
}