Task

You will solve the former “Head and Tail” task (from Chapter 16) using the conditional operator (see Figure 19-1).

Figure 19-1 Using the conditional operator

Solution

Here’s the code:

static void Main(string[] args)
{
    // Random number generator
    Random randomNumbers = new Random();

    // Random number 0/1 and its transformation
    int randomNumber = randomNumbers.Next(0, 1 + 1);
    string message = randomNumber == 0 ? "Head tossed" : "Tail tossed";
    Console.WriteLine(message);

    // Waiting for Enter
    Console.ReadLine();
}

Discussion

The conditional operator (?:) syntax looks like this:

• condition ? yesValue : noValue

The result of such an expression is as follows:

• yesValue if the condition holds (is fulfilled)

• noValue otherwise

Task

The task is to write a program for summary evaluation of a student (see Figure 19-2). The user enters grades from four subjects (in the range 1 to 5, with 1 being the best). The user also specifies whether the student being considered had some unexcused absences or not. The program then gives a summary evaluation, which is a kind of overall score.

• Excellent

• Good

• Failed

Figure 19-2 Summary evaluation of a student

Details

I emphasized in Chapter 18 that to be able to program anything, you need to exactly understand the task being solved. In the current exercise, you need to specify the exact criteria for summary evaluation.

A student has an Excellent evaluation when

• The arithmetic average of all the grades is not higher than 1.5

• The student does not have any grade worse than 2

• The student does not have any unexcused absences

The student is considered Failed when at least one of her grades is 5.

In all other cases, the summary evaluation is Good.

You can probably guess now that the program is not going to be trivial.

Solution

Here’s the code:

static void Main(string[] args)
{
    // 1. PREPARATIONS
    string errorMessage = "Incorrect input";
    int mathematics, informationTechnology, science, english;
    bool hasUnexcusedAbsences;

    // 2. INPUTS
    try
    {
        Console.WriteLine("Enter grades from individual subjects:");

        Console.Write("Mathematics: ");
        string input = Console.ReadLine();
        mathematics = Convert.ToInt32(input);
        if (mathematics < 1 || mathematics > 5)
        {
            Console.WriteLine(errorMessage);
            return;
        }

        Console.Write("Information technology: ");
        input = Console.ReadLine();
        informationTechnology = Convert.ToInt32(input);
        if (informationTechnology < 1 || informationTechnology > 5)
        {
            Console.WriteLine(errorMessage);
            return;
        }

        Console.Write("Science: ");
        input = Console.ReadLine();
        science = Convert.ToInt32(input);
        if (science < 1 || science > 5)
        {
            Console.WriteLine(errorMessage);
            return;
        }

        Console.Write("English: ");
        input = Console.ReadLine();
        english = Convert.ToInt32(input);
        if (english < 1 || english > 5)
        {
            Console.WriteLine(errorMessage);
            return;
        }

        Console.Write("Any unexcused absences? (yes/no): ");
        input = Console.ReadLine();
        input = input.ToLower(); // not distinguishing upper/lower
        if (input != "yes" && input != "no")
        {
            Console.WriteLine(errorMessage);
            return;
        }
        hasUnexcusedAbsences = input == "yes";
    }
    catch (Exception)
    {
        Console.WriteLine(errorMessage);
        return;
    }

    // 3. EVALUATION
    // You need arithmetic average of all the grades
    double average = (mathematics + informationTechnology + science + english) / 4.0;
    string message;

    // Testing all conditions for excellence
    if (average < 1.5001 &&
        mathematics <= 2 && informationTechnology <= 2 &&
        science <= 2 && english <= 2 &&
        !hasUnexcusedAbsences)
    {
        message = "Excellent";
    }
    else
    {
        // Here you know the result is not excellent, so testing the other two possibilities
        if (mathematics == 5 || informationTechnology == 5 ||
            science == 5 || english == 5)
        {
            message = "Failed";
        }
        else
        {
            message = "Good";
        }
    }

    // 4. OUTPUT
    Console.WriteLine("Summary evaluation: " + message);

    // Waiting for Enter
    Console.ReadLine();
}

Discussion

The following sections explain the program.

hasUnexcusedAbsences = input == "yes";

average < 1.5001

average <= 1.5

Task

I will show you how to test the second character of the entered text. Let’s say a product label has to always have a capital X in the second position (see Figure 19-3 and Figure 19-4).

Figure 19-3 Testing the second character, correct

Figure 19-4 Testing the second character, incorrect

Why is such a test so important that I have decided to get you acquainted with it? You need to test first whether the second character exists at all. This is what you will often meet; you will not be able to test something until you have found that something exists!

In this case, the program must not crash upon empty or too short input (see Figure 19-5).

Figure 19-5 Incorrect label, not crashing

Solution

Here’s the code:

static void Main(string[] args)
{
    // Input
    Console.Write("Enter product label: ");
    string label = Console.ReadLine();

    // Evaluating
    if (label.Length >= 2 && label.Substring(1, 1) == "X")
    {
        Console.WriteLine("Label is OK");
    }
    else
    {
        Console.WriteLine("Incorrect label");
    }

    // Waiting for Enter
    Console.ReadLine();
}

Discussion

The following sections explain the program .

if (label.Length >= 2 && label.Substring(1, 1) == "X")