Loops

Here is the code from class. It is, of course, not a coherent program just a set of examples

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace LoopExamples
{
    class Program
    {
        static void Main(string[] args)
        {
            //this is a simple for loop
            //first you set the counter, then you set
            //the limit, then you increment (++) the counter
            for (int counter = 0; counter < 20; counter++)
            {
                Console.WriteLine(counter);
            }

            //this is a for loop that outputs the prime numbers
            //from the previous assignment
            for (int i = 1; i < 41; i++)
            {
                int prime = i * i - i + 41;
                Console.WriteLine(prime);
            }

            //your can use a variable for the loop limit
            Console.WriteLine("how many loops do you want to do?");
            int number = int.Parse(Console.ReadLine());

            //avoid an infinite loop--infinite loops result
            //when the end condition will never be met
            for (int x = 1; x < number; x--)//decrement -1
            {
                Console.WriteLine(x);
                if (x == -10)
                {
                    break;
                }

            }

            //you can use other operators that ++ or --
            //this one counts up by 3s
            for (int i = 1; i < 20; i += 3)
            {
                Console.WriteLine(i);
            }

            // +=, -=, *=, /=, %=
            //number -= 2  equivalent to number = number - 2
           // number *= 2 equivelant to number = number * 2

            Console.WriteLine("how many numbers do you want to enter");
            int num = int.Parse(Console.ReadLine());
            //I declare these outside the loop so that I can use them
            //outside--if I declared them in the loop they would 
            //have the "scope" of the loop. In general a variable has the scope
            //of the block "{}" it is declared in
            double sum = 0;
            double average = 0;

            for (int i = 1; i <= num; i++)
            {
                Console.WriteLine("enter a number");
                double myNumber = double.Parse(Console.ReadLine());
                sum += myNumber;

            }

            Console.WriteLine("the sum is {0}", sum);
            average = sum / num;
            Console.WriteLine("The average is {0}", average);

            //a while loop continues looping until the critera
            //set at the beginning is no longer true

            string quit = "no";
           //Equals is equivalent to "==" but works better with strings
            while (quit.Equals("no") || quit.Equals("No"))
            {
                Console.WriteLine("Are your ready to quit 'yes/no");
                quit = Console.ReadLine();
                quit = quit.ToLower();//this forces everything to lower case
            }

            bool goodNumber = false;
            int number2=0;
            //this loops until the user enters a good number
            while (goodNumber == false)
            {
                Console.WriteLine("enter a valid number");
                goodNumber = int.TryParse(Console.ReadLine(), out number2);
            }

            Console.WriteLine("Your Number is {0}", number2);

            // a do while loop is like a while loop except it checks its
            //criteria at the end. that means it is guaranteed to execute
            //at least once
            do
            {
                Console.WriteLine("enter a valid number");
                goodNumber = int.TryParse(Console.ReadLine(), out number);

            } while (goodNumber == false);




            Console.ReadKey();

        }
    }
}