Task

You will write program that accepts a decimal number from the user and repeats it immediately on the screen (see Figure 9-1).

Figure 9-1 The final program

Solution

There are two differences between the input of whole and decimal numbers.

• You convert text input into a corresponding number by calling the Convert.ToDouble method.

• To store a converted number, you use a variable of type double.

Here is the code:

static void Main(string[] args)
{
    // Decimal input
    Console.Write("Enter a decimal number: ");
    string input = Console.ReadLine();
    double decimalNumber = Convert.ToDouble(input);

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

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

Task

The task is to write a program that reads a decimal number with two fixed-language settings, American and Czech.

Solution

To work with specific localizations, use the CultureInfo object. Also, please do not forget to insert the using System.Globalization; line at the top of your source code.

Here is the code:

static void Main(string[] args)
{
    // AMERICAN
    CultureInfo american = new CultureInfo("en-US");
    try
    {
        // Input
        Console.Write("Enter American decimal number: ");
        string input = Console.ReadLine();
        double number = Convert.ToDouble(input, american);

        // Output
        Console.WriteLine("You have entered " + number);
    }
    catch (Exception)
    {
        // Error message
        Console.WriteLine("Incorrect input");
    }

    // CZECH
    CultureInfo czech = new CultureInfo("cs-CZ");
    try
    {
        // Input
        Console.WriteLine();
        Console.Write("Enter Czech decimal number: ");
        string input = Console.ReadLine();
        double number = Convert.ToDouble(input, czech);

        // Output
        Console.WriteLine("You have entered " + number);
    }
    catch (Exception)
    {
        // Error message
        Console.WriteLine("Incorrect input");
    }

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

Testing and Conclusions

The following sections cover how this works.

Test with a Decimal Point

Run your program and enter a number with a decimal point twice (see Figure 9-2).

Figure 9-2 Entering two numbers with decimal points

The program accepts a point as a decimal separator when using the American localization. At the same time, it refuses a decimal point when using the Czech localization since a point is not a valid decimal separator in Czech.

Test with a Decimal Comma

Run your program again and this time enter a number with decimal comma twice (see Figure 9-3).

Figure 9-3 Entering a number twice with a comma

Now the program accepts the decimal comma as a valid separator in Czech.

When using the American localization, the program does not see any decimal number. It simply ignores the comma and converts the user input into a whole number!

Task

You will write a program that accepts two decimal numbers from the user and displays the results of their addition, subtraction, multiplication, and division (see Figure 9-4).

Figure 9-4 Doing basic arithmetic

Solution

Here is the code:

static void Main(string[] args)
{
    // Inputs
    Console.Write("Enter first number: ");
    string input1 = Console.ReadLine();
    double number1 = Convert.ToDouble(input1);

    Console.Write("Enter second number: ");
    string input2 = Console.ReadLine();
    double number2 = Convert.ToDouble(input2);

    // Calculations
    double sum = number1 + number2;
    double difference = number1 - number2;
    double product = number1 * number2;
    double quotient = number1 / number2;

    // Output
    Console.WriteLine("Sum is " + sum);
    Console.WriteLine("Difference is " + difference);
    Console.WriteLine("Product is " + product);
    Console.WriteLine("Quotient is " + quotient);

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

Task

To get you a taste of the mathematical functions available, you will calculate the sine and the square root of the entered numbers in this task (see Figure 9-5).

Figure 9-5 Calculating the sine and the square root

Solution

Here is the code:

static void Main(string[] args)
{
    // Input of angle
    Console.Write("Enter an angle in degrees: ");
    string input = Console.ReadLine();
    double angleInDegrees = Convert.ToDouble(input);

    // Calculation and output of sine value
    double angleInRadians = angleInDegrees * Math.PI / 180;
    double result = Math.Sin(angleInRadians);
    Console.WriteLine("Sine of the angle is: " + result);

    // Input of a positive number
    Console.WriteLine();
    Console.Write("Enter a positive number: ");
    input = Console.ReadLine();
    double number = Convert.ToDouble(input);

    // Calculation and output of square root
    Console.WriteLine("Square root of the number is: " + Math.Sqrt(number));

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

Discussion

Note the following:

• To calculate values of mathematical functions , you use the Math object; it contains many useful functions, not just the ones shown.

• The Sin function requires the angle to be specified in radians. If your input is in degrees, which is usually the case, you need to make a conversion.

• With the second input (a number), you “recycled” the variable input that was already used before; you used it a second time since you did not need the stored value anymore. However, this means you do not declare the variable a second time.

• You do not have to “recycle” variables; variables are not precious resources these days. But you can if you want, which is what I showed you.

• Contrary to the first calculation, you did not store the calculated square root into any variable. You directly wrote the calculation into the output statement (WriteLine).

• If the user enters a negative number, its square root cannot be calculated , and the result becomes NaN (which means “not-a-number”).

Task

In this exercise, you will explore “normal” and integer divisions of the two numbers entered by the user (see Figure 9-6).

Figure 9-6 Exploring “normal” and integer divisions

Solution

Here is the code:

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

    Console.Write("Enter 2. whole number (divisor): ");
    string input2 = Console.ReadLine();
    int number2 = Convert.ToInt32(input2);

    // Integer calculations
    int integerQuotient = number1 / number2;
    int remainder = number1 % number2;

    // "Normal" calculations
    double number1double = number1;
    double number2double = number2;
    double normalQuotient = number1double / number2double;

    // Alternatively
    double normalQuotientAlternatively = (double)number1 / (double)number2;

    // Outputs
    Console.WriteLine("-----------------");
    Console.WriteLine("Integer quotient: " + integerQuotient +
        " with remainder " + remainder);
    Console.WriteLine(""Normal" quotient : " + normalQuotient);
    Console.WriteLine(""Normal" quotient (alternatively): " + normalQuotientAlternatively);

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

Discussion

Note the following:

• To compute the remainder , you use the % operator (percent sign).

• I have shown you two ways to force the entered values to doubles to achieve “normal” division.

  • Assignment to variables of type double.

  • Type cast to double; you prepend the value with the target type in parentheses.