//Programmer: Hashan Undugodage

//Date: April 20--April 26

//Program: Prime Number Calculator

//Program Description: To evaluate the user input to test if it is a prime or composite and number 

//and have the option to express, all primenumbers from 1-100,000

​

​

using System;

​

public class Program

{

    public static void Main()

    {

        start: //Checkpoint (To Come back to, for error checking, and to play again etc)

        // Print a header for the program

        Console.WriteLine("{0,-2}{1,-20}{2}","|", "Prime Number Tester","|");

        Console.WriteLine(new string('-', 23));

​

        // Prompt the user to enter a positive integer

        Console.WriteLine("Please Enter a Positive Integer:");

        numero: //Checkpoint

        int number;

        // Read the user's input and validate it (! is utilize to say if the statement is not true print out error checking)

        if (!int.TryParse(Console.ReadLine(), out number) || number <= 0)

        {

            Console.WriteLine("Incorrect Value. Please enter a positive integer.");

            goto numero;

        }

​

        // Check whether the input number is prime or composite

        bool isPrime = true;

​

        // Loop through all possible factors up to the square root of the number

        for (int count = 2; count <= Math.Sqrt(number); count++)

        {   

            //Check to see if a prime number utilizing % to get the remainder

            if (number % count == 0)

            {

                // If the number has a factor other than 1 and itself, it is composite

                isPrime = false;

                break;

            }

        }

​

        // Print the result to the console

        if (isPrime)

        {

            Console.WriteLine(number + " is a prime number.");  //If the compiler decides the the inputed number "isPrime" then print out prime

        }

        else

        {

            Console.WriteLine(number + " is a composite number."); //Otherwise it is composite

        }

​

        // Show the list of prime numbers from 1 to 100,000

        Console.WriteLine("Enter 1 to see all primes  Numbers from 1-100,000, enter 2 exit program:");

        choice: //Checkpoint

        int choices;

        if (!int.TryParse(Console.ReadLine(), out choices) || (choices != 1 && choices != 2)) //If the inputed value is not 1,2 and is not an integer:

        {

            Console.WriteLine("Incorrect choice. Please enter 1 or 2.");

            goto choice;

        }

        if (choices == 2) //If the user input the 2nd option, the program ends, however the user can play again if they want to

        {

            responses: //Checkpoint

            Console.WriteLine("Do you wanna go again, Y/N");

            char response;

             if (!Char.TryParse(Console.ReadLine().ToLower(), out response) || (response != 'y' && response != 'n')) //If the inputed value is not n or why, and is not an character:

             { //.To Lower, turn the char into lowercase if capatlized

                Console.WriteLine("Invalid Input, try again");

                goto responses; //Go to checkpoint

            }

            if (response == 'y') //Restart Program

            {

                goto start;

            }

            else if (response == 'n') //End Program

            {

                return;

            }

        }

            else if (choices == 1) //Find the prime numbers from 1-100,000 (Bonus)

            {

                // Loop through all numbers from 2 to 100,000

                for (int num = 2; num <= 100000; num++) {

                    bool isPrimeNum = true;

​

                    // Loop through all possible factors up to the square root of the number

                    for (int factors  = 2; factors <= Math.Sqrt(num); factors++) {

                        if (num % factors == 0) {

                            // If the number has a factor other than 1 and itself, it is composite

                            isPrimeNum = false;

                            break;

                        }

                    } 

​

                    // If the number is prime, print it to the console

                    if (isPrimeNum) {

                        Console.WriteLine(num);

                    //Programmmr Note, this program aided me learn, how a composite, and prime differnumber, utilizing different equations, and the forloop

                    //to go through all possibilities.

                    }

                }

            }

        }

    }

​