Displaying text in Ruby is simple. Try entering the following at the command prompt:

irb(main):001:0> puts "Hello World"

The puts method (short for outPUT a String) simply displays a string on the screen. Notice the string is contained in quotation marks; otherwise, both Hello and World would be interpreted as variables. Variables are displayed on the screen using similar syntax, except without quotation marks:

irb(main):002:0> text = "Hello World"
=> "Hello World"
irb(main):003:0> puts text
=> Hello World

This example stores the string “Hello World” in a variable named text and then displays the value stored in the text variable using the puts method. This method is not limited to strings and can be used with other classes including integers, floats, and Booleans.

The use of classes to define data types means a variety of methods can be done for each type. For example, x.length indicates the size of a string when x is defined as a string.

Displaying user input in Ruby is almost as easy as displaying output. Try entering the following in the command prompt:

irb(main):001:0> age_input = gets

The gets method (short for GET a String from the user) stops the program and waits for the user to type some text and then press Enter. The text typed by the user will be stored as a string in a variable called age_input. Due to the nature of the gets method, the value stored in age_input will be a string, but you need an integer if you wish to mathematically manipulate it. We create another variable age and set it equal to the integer value of the user’s input by converting the string age_input to an integer. This is done by issuing the following command:

irb(main):002:0> age = age_input.to_i

The method to_i converts age_input to an integer.

Now that you have learned how to display text and request user input, you can develop a program that calculates the area of a rectangle. Try using the problem-solving approach discussed in Chapter 1 to create this program.

Ask yourself key questions that must be answered to properly design the program:

Before writing out the problem, remember that the input method stores user input as strings, so we need to convert the lengths (which are stored as strings) to integers before performing mathematical operations with them.

The equation for the area of a rectangle is the product of its length and width. Although it does not affect this equation, remember that the rules for order of operations apply in Ruby. To change the order of operations, use parentheses.

See Example 3-1. In the figure, as with all other program illustrations, the line numbers are not part of the code; they are added strictly for explanatory purposes. In line 8, we are printing an integer represented in the variable area. This differs from the printing of character strings in lines 1 and 3. Ruby automatically determines the data type, if it can. This is called dynamic or “duck” typing. This functionality is helpful; however, as you will see, automatic type determination can introduce problems. In this example, though, it helps in that puts area is mapped to puts area.to_s. Note that generally speaking, the .to_* method is a type conversion operation where the target type is represented by the * (a wildcard). For example, you have now seen conversion to integer (to_i) and to string (to_s).

    1 puts "What is the length?"	# Ask for the length 
    2 length_input = gets		# Stores the length 
    3 puts "What is the width?"	# Ask for the width 
    4 width_input = gets		# Stores the width 
    5 length  = length_input.to_i	# Convert length to integer 
    6 width = width_input.to_i	# Convert width to integer 
    7 area = length * width		# Calculate rectangle area 
    8 puts area			# Display area 

Similarly those who are adventurous can type the code lines from step 3 into a file and run the code from there. For those who are unsure, no worries; we address files later on. For now, simply see if you get the desired results; if not, make sure you typed everything correctly.

If it works, congratulations! You have just created a program that calculates the area of a rectangle.