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Next: Logic >>

Input and Output

  • Computers have many senses -- keyboard, mouse, network card, digital camera, etc. Collectively, these are called INPUT.

  • Computers can also express themselves in many ways -- text, graphics, sound, network, printers, etc. Collectively, these are called OUTPUT.

  • Input and Output together are called I/O.

Terminal I/O

  • In Ruby,

    • puts means "print a line to the terminal"
    • gets means "read a line from the terminal"
  • gets reads all the characters from the keyboard and puts them into a new string, until you press RETURN

LAB: Hello, friend!

  1. Open hello.rb in your text editor
  2. Change it to contain the following code:

    puts "What is your name?"
    name = gets
    puts "Hello, " + name + "!"
    
  3. Save the file and switch back to the terminal

  4. Run the program using ruby hello.rb

  5. Type in your name and press the RETURN (or ENTER) key

What happens? Is this what you expected?

Yikes!

  • Uh-oh! We've got trouble... what is that exclamation point doing way down there?

  • The first thing to do is DON'T PANIC!

  • You are totally going to figure this out.

  • And even if you don't, you haven't actually broken anything.

  • In fact, it's really hard to break a computer, so just stay calm.

Breathe

  • In through the nose...
  • Out through the mouth...
  • In through the nose...
  • Ahhhhhhhh.

Let's fix this

  • Have you figured out what the problem is?
  • If not, I'll tell you on the next slide.
  • Take a second and try to figure it out first. I'll wait.

The newline character

  • Here's a fun fact:
  • In addition to letters, numbers, and punctuation, computers also store other keys inside strings
  • Among these CONTROL CHARACTERS is the one that represents the RETURN KEY
  • This character's name is NEWLINE
  • Every time you use gets, Ruby reads all the characters, including the newline!

Strip it

  • Fortunately, there's an easy fix
  • If you send the message strip to a string, it will remove all SPACES and NEWLINES from both ends

LAB: fixing Hello, Friend

  • Change the program to look like this:

    puts "What is your name?"
    name = gets.strip
    puts "Hello, " + name + "!"
    
  • Run it and make sure it works OK

LAB: Capitalization

  • What happens if you type your name in all lowercase?
  • Make the program capitalize your name for you even if you forget.

LAB: Crazy Name

  • Now go crazy and make it do all sorts of silly things to your name!

LAB: Full Name

  • Write a program named name.rb that asks two things:
    1. Your first name
    2. Your last name
  • Then it says hello to the user by her full name.
  • Run the program by typing ruby name.rb on the command line.

CONGRATULATIONS!

You just wrote a program!

You are now officially a coder. HIGH FIVE!

Lab: Name Length

  • Change name.rb so it also prints the number of characters in the user's name.
  • For instance:

    What is your first name?
    Alex
    What is your last name?
    Chaffee
    Hello, Alex Chaffee! 
    Your name is 11 characters long.
    
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