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While loop

The while loop is one of the simplest and most commonly used control structures in programming. Its syntax is as follows:

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while (condition)
{
    // body of the loop
}

Understanding the While Loop

In this context, the condition is any expression that evaluates to a Boolean result, meaning it can be either true or false. The loop will continue to execute as long as the condition remains true. Once the condition becomes false, the loop terminates. It's important to note that if the condition is initially false, the loop body will not execute at all. This characteristic distinguishes the while loop from the do ... while loop, which guarantees at least one execution of the loop body.

Example: Calculating the Average of a Series of Numbers

Let’s look at a practical example where we use a while loop to calculate the average of a series of numbers. 

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// Design an algorithm and write a program to find the average of a series of numbers.
using System;

namespace AverageCalculator
{
    class Program
    {
        static void Main(string[] args)
        {
            double average;
            double sum = 0;
            double value;
            int count = 0;
            bool finished = false;

            while (!finished)
            {
                Console.Write("Enter number (0 to quit) > ");
                value = Convert.ToDouble(Console.ReadLine()); // Changed to Convert.ToDouble for more accurate inputs
                if (value == 0)
                {
                    finished = true; // Ends the loop if the user enters 0
                }
                else
                {
                    count++; // Increment the count of valid entries
                    sum += value; // Add the entered value to the sum
                }
            }

            if (count > 0) // Check to avoid division by zero
            {
                average = sum / count; // Calculate the average
                Console.WriteLine($"Average = {average}");
            }
            else
            {
                Console.WriteLine("No numbers were entered to calculate an average.");
            }

            Console.Write("Press any key to quit ...");
            Console.ReadKey();
        }
    }
}

Code Explanation

  • Lines 14, 16: The finished Boolean variable acts as the condition for the loop. The loop will continue to run as long as finished is not true.
  • Line 22: When the user enters 0, finished is set to true, terminating the loop. If the input is non-zero, the program increments the count and adds the input value to sum.
  • Line 30: Once the loop ends, the average is calculated using sum divided by count. A check is included to ensure that at least one valid number was entered to avoid division by zero.

Note

If the condition is false when the loop is first encountered, the loop will not execute at all. This property makes the while loop a top-tested loop, as the condition is evaluated before each iteration.

Alternative Exit Conditions

An alternative approach could involve asking the user for the total number of values to be averaged. In this case, the loop would need a counter variable to track how many numbers have been entered, allowing it to terminate gracefully once the specified number is reached.