Task

You will write a program that accepts a single line of text from the user and immediately repeats the inputted text to the output (see Figure 8-1).

Figure 8-1 The completed program

Solution

Here is the code:

static void Main(string[] args)
{
    // Reading single line of text (until user presses Enter key)
    string input = Console.ReadLine();

    // Outputting the input
    Console.WriteLine(input);

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

When you launch the program using the F5 key, you will see an empty screen. Enter a sentence and send it to the program using the Enter key .

Task

You will modify the previous program in a way to give the user a hint about what she is supposed to do (see Figure 8-2).

Figure 8-2 The improved program

Solution

Here is the code:

static void Main(string[] args)
{
    // Hinting user what we want from her
    Console.Write("Enter a sentence (and press Enter): ");

    // Reading line of text
    string input = Console.ReadLine();

    // Repeating to the output
    Console.WriteLine("You have entered: " + input);

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

Discussion

Console.Write does not transfer the cursor to the next line, contrary to Console.WriteLine, which you have been using exclusively up to now.

Task

You will write a program that takes a number from the user, stores it in a numeric variable, and finally repeats it to the user (see Figure 8-3).

Figure 8-3 Reading a number from the screen

Solution

Console.ReadLine always reads text even if its meaning is a number. If you want to hold a real number (i.e., a value of the int type), you have to manufacture it using the Convert.ToInt32 call.

static void Main(string[] args)
{
    // Prompting the user
    Console.Write("How old are you? ");

    // Reading line of text
    string input = Console.ReadLine();

    // CONVERTING TO NUMBER (of entered text)
    int enteredNumber = Convert.ToInt32(input);

    // Output of entered number
    Console.WriteLine("Your age: " + enteredNumber);

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

Discussion

Strictly speaking, you have not actually needed a real number yet since you have not made any calculation on the numbers. However, this will change in next exercise. Here you were exploring numeric input in the simplest possible form.

Task

You will write a program that accepts a year of birth from the user and calculates her age afterward (see Figure 8-4).

Figure 8-4 Calculating an age

Solution

Here is the solution:

static void Main(string[] args)
{
    // Prompting the user
    Console.Write("Enter year of your birth: ");

    // Reading line of text
    string input = Console.ReadLine();

    // CONVERING TO NUMBER (of entered text)
    int yearOfBirth = Convert.ToInt32(input);

    // Finding this year
    DateTime today = DateTime.Today;
    int thisYear = today.Year;

    // Calculating age
    int age = thisYear - yearOfBirth;

    // Outputting the result
    Console.WriteLine("This year you are/will be: " + age);

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

Task

You will write a program that accepts a number from the user. After that, it displays a number that is greater by ten than the one entered (see Figure 8-5).

Figure 8-5 Adding ten to a number

Solution

Here is the code:

static void Main(string[] args)
{
    // Number input
    Console.Write("Enter a number: ");
    string input = Console.ReadLine();
    int number = Convert.ToInt32(input);

    // Calculating
    int result = number + 10;

    // Displaying the result
    Console.WriteLine("Number greater by ten: " + result);

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

Task

You will write a program that sums two numbers entered by the user (see Figure 8-6).

Figure 8-6 Summing two numbers

Solution

Here is the code:

static void Main(string[] args)
{
    // Input of 1. number
    Console.Write("Enter 1. number: ");
    string input1 = Console.ReadLine();
    int number1 = Convert.ToInt32(input1);

    // Input of 2. number
    Console.Write("Enter 2. number: ");
    string input2 = Console.ReadLine();
    int number2 = Convert.ToInt32(input2);

    // Calculating
    int result = number1 + number2;

    // Result output
    Console.WriteLine("Sum of entered numbers is: " + result);

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

Task

In this exercise, you will modify the previous program so that it correctly handles non-numeric input from the user (see Figure 8-7).

Figure 8-7 Providing feedback for an error

Solution

Leave your last project opened, or open it again if you closed it already. In what follows, you will edit the project’s Program.cs source code; specifically, you will insert a try-catch construct in an appropriate place.

Using your mouse, select the whole interior of Main excluding the last statement (waiting for Enter), exactly as shown in Figure 8-8. After that, right-click anywhere in the selected block and choose Snippet and then Surround With from context menu.

Figure 8-8 Choosing Surround With

In the small pane that pops up, select Try (see Figure 8-9).

Figure 8-9 Selecting Try

What Happened

What happened? Visual Studio wrapped the selected lines into the try block, which consists of the word try and a pair of curly brackets. It also inserted a catch block, which includes the word catch and a pair of curly brackets, after the try block.

Interior of the catch Part

Delete the statement throw inside the catch block and enter the following statement instead:

Console.WriteLine("Incorrect input - cannot calculate");                  

Complete Solution

Here is the complete solution:

static void Main(string[] args)
{
    try
    {
        // Input of 1. number
        Console.Write("Enter 1. number: ");
        string input1 = Console.ReadLine();
        int number1 = Convert.ToInt32(input1);

        // Input of 2. number
        Console.Write("Enter 2. number: ");
        string input2 = Console.ReadLine();
        int number2 = Convert.ToInt32(input2);

        // Calculating
        int result = number1 + number2;

        // Result output
        Console.WriteLine("Sum of entered numbers is: " + result);
    }
    catch (Exception)
    {
        Console.WriteLine("Incorrect input - cannot calculate");
    }

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

Testing

You can test your program both for numeric input and for nonsense now.

Explanation

Statements in a try block are executed in a kind of “trial mode.”

• When all of them succeed, execution in the try block proceeds normally, and the catch block is skipped afterward.

• When a statement fails, the rest of the try block is skipped, and statements in the catch block are executed instead.