Task

In the section “Choosing the Number of Repetitions,” the user was allowed to vary the number of repetitions of a given sentence. Now you will allow the user to vary the sentence itself (see Figure 21-1).

Figure 21-1 Varying a sentence

Solution

Here’s the code:

static void Main(string[] args)
{
    // Inputs
    Console.Write("Enter text to repeat: ");
    string textToRepeat = Console.ReadLine();

    Console.Write("Enter number of repetitions: ");
    string input = Console.ReadLine();
    int howManyTimes = Convert.ToInt32(input);

    // Output
    for (int count = 0; count < howManyTimes; count++)
    {
        Console.WriteLine(textToRepeat);
    }

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

Task

You will write a program that alternates between two tasks in a to-do list (see Figure 21-2).

Figure 21-2 Alternating between two tasks

First Solution

The first solution is based on distinguishing whether the loop’s control variable, which is running from 1 to 10, is odd or even. When it is odd, you display “Learning.” When it is even, you display “Dating.”

An odd/even test will be performed by checking the remainder after integer division by 2. Just to remind you, the remainder is calculated using the percent sign (%) operator in C#.

static void Main(string[] args)
{
    // Output
    Console.WriteLine("My main to-do list:");

    for (int taskNumber = 1; taskNumber <= 10; taskNumber++)
    {
        string taskText = taskNumber % 2 != 0 ? "Learning" : "Dating";
        Console.WriteLine(taskNumber.ToString() + ". " + taskText);
    }

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

Second Solution

The second solution toggles a Boolean value back and forth.

You have a bool-typed variable that you toggle from true to false, and vice versa, in every turn of a loop. When the variable equals to true, you display the first text. When it is false, you display the second one.

static void Main(string[] args)
{
    // Preparations
    Console.WriteLine("My main to-do list:");
    bool learning = true;

    for (int taskNumber = 1; taskNumber <= 10; taskNumber++)
    {
        // Output
        string taskText = learning ? "Learning" : "Dating";
        Console.WriteLine(taskNumber.ToString() + ". " + taskText);

        // Toggling of the flag
        learning = !learning;
    }

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

Third Solution

The third approach to the solution is to repeat the loop five times rather than ten times and to perform both “odd activity” and “even activity” in a single turn of the loop.

Here’s the code:

static void Main(string[] args)
{
    // Preparations
    Console.WriteLine("My main to-do list:");
    int taskNumber = 1;

    for (int coupleCount = 0; coupleCount < 5; coupleCount++)
    {
        // Couple output and adjusting task number
        Console.WriteLine(taskNumber.ToString() + ". Learning");
        taskNumber++;
        Console.WriteLine(taskNumber.ToString() + ". Dating");
        taskNumber++;
    }

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

Task

You will write a program that plays a specified number of rounds of the rock-scissors-paper game with the user (see Figure 21-3).

Figure 21-3 The game

Scoring will be similar to chess: one point for a victory and half a point for a tie.

Solution

Here’s the code:

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

    double playerPoints = 0;
    double computerPoints = 0;

    int rock = 1, scissors = 2, paper = 3;

    // Inputs
    Console.Write("Enter your name: ");
    string playerName = Console.ReadLine();

    Console.Write("Enter number of game rounds: ");
    string input = Console.ReadLine();
    int totalRounds = Convert.ToInt32(input);

    Console.WriteLine();

    // Individual rounds
    for (int roundNumber = 0; roundNumber < totalRounds; roundNumber++)
    {
        // Computer chooses
        int computerChoice = randomNumbers.Next(1, 3 + 1);

        // Player chooses
        Console.Write("Enter R or S or P: ");
        string playerInput = Console.ReadLine();
        string playerInputUppercase = playerInput.ToUpper();
        int playerChoice = playerInputUppercase == "R" ?
            rock : (playerInputUppercase == "S" ? scissors : paper);

        // Round evaluation
        string message = "";
        if (computerChoice == rock && playerChoice == scissors ||
            computerChoice == scissors && playerChoice == paper ||
            computerChoice == paper && playerChoice == rock)
        {
            // Computer won
            computerPoints += 1;
            message = "I won";
        }
        else
        {
            // Tie or player won
            if (computerChoice == playerChoice)
            {
                // Tie
                computerPoints += 0.5;
                playerPoints += 0.5;
                message = "Tie";
            }
            else
            {
                // Player won
                playerPoints += 1;
                message = "You won";
            }
        }

        // Round output
        string playerChoiceInText = playerChoice == rock ?
            "Rock" : (playerChoice == scissors ? "Scissors" : "Paper");
        string computerChoiceInText = computerChoice == rock ?
            "Rock" : (computerChoice == scissors ? "Scissors" : "Paper");
        Console.WriteLine(playerName + ":Computer - " +
            playerChoiceInText + ":" + computerChoiceInText);
        Console.WriteLine(message);
        Console.WriteLine();
    } // End of loop for game round

    // Game evaluation
    Console.WriteLine("GAME OVER - OVERALL RESULT");
    Console.WriteLine(playerName + ":Computer - " +
        playerPoints.ToString() + ":" + computerPoints.ToString());

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

Discussion

Note the following:

• The computer “chooses” using random numbers: 1 for rock, 2 for scissors, and 3 for paper.

• For the sake of simplicity, when the user enters something other than R, S, or P, you take it as “paper.”

• You do not distinguish between lowercase and uppercase in user input.

• In several places, threefold branching is solved using two nested conditional (ternary) operators rather than using two nested if-elses. Note carefully how noValue of the first conditional operator is specified using another conditional operator, which is enclosed in parentheses.

• If you do not like the conditional (ternary) operator, simply do not use it. It is just a shortcut of a special if-else case. I personally like it very much, so I use it frequently.