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A simple adding machine.

Adder

Try

Watch this video to learn about the new concepts shown in the program:

Knowledge organiser

A “sentinel” is a dummy value that is used to terminate a while iteration. Most commonly used with Console.ReadLine() to mark the end of an input stream.

You have to be careful that the sentinel value is not valid data.

You can use true as a value to create an infinite loop. E.g. while (true) will never end because true is always true. This can be useful if you don’t want your program to end unless the user closes the program.

Investigate

Questions to think about with this program to check your understanding:

Relation question

Explain why the Console.ReadLine() call:

string data = Console.ReadLine();

must be inside the while (!complete) loop and not before it.

Reveal answer

You want the user to be able to keep entering numbers until they enter the sentinel value, so the input must be inside the loop.

Approach question

What is the problem with using zero as the sentinel value?

Reveal answer

It means that zero can never be input as a valid number. This is a problem if you want the data set to include zeros for the purpose of calculating the average. A better approach (used here) is to read the input as a string first, check if it equals the sentinel character, and only then convert it to a double. The sentinel letter becomes the terminator and not the number zero.

Make

Change the program so that it:

  1. Uses the letter “e” as the sentinel value instead of zero. Note you will need to read the input as a string first because a letter cannot be cast to a double.
  2. Outputs the lowest (bottom) number too.

Hint

The lowest number will need to be initialised to be the first number that is input.

Typical inputs and outputs from the program would be:

Enter number:
4
Enter number:
2
Enter number:
8
Enter number:
6
Enter number:
e
Total: 20.0 Top: 8.0 Bottom: 2.0 Ave: 5.0
🆘 If you're really stuck, use this Parsons code sorting exercise
Complete program
// Adder program

using System;

class Submission
{
---
    // -------------------------
    // Subprograms
    // -------------------------
    // A simple adding machine
    static void adder()
    {
---
        double total = 0;   // Total
        double top = 0;     // Highest number
        double bottom = 0;  // Lowest number
        int count = 0;      // Count of numbers
        double ave = 0;     // Average
        bool complete = false;
---

        // Repeat until sentinel value entered 'e'
        while (!complete)
        {
---
            Console.WriteLine("Enter number:");
            string data = Console.ReadLine();
---

            // Add the number if it is not the sentinel
            if (data != "e")
            {
---
                double number = Convert.ToDouble(data);
                total = total + number;
                count = count + 1;
---
                // Set the highest number
                if (number > top)
                {
---
                    top = number;
---
                }
---
                // Set the lowest number
                if ((count == 1) || (number < bottom))
                {
---
                    bottom = number;
---
                }
---
            }
---
            else {
                complete = true;
                // Prevent a division by zero error
                if (count > 0)
                {
---
                    ave = total / count;
---
                }
---
                else
                {
---
                    ave = 0;
---
                }
---
            }
---
        }
---
        Console.WriteLine($"Total: {total} Top: {top} Bottom: {bottom} Ave: {ave}");
---
    }
---


    // -------------------------
    // Main program
    // -------------------------
    public static void Main(string[] args)
    {
---
        adder();
---
    }
---
}