String Concatenation

IRB

• IRB stands for "Interactive RuBy".
• You can run it by clicking in your console or terminal and typing irb at the system prompt.
• When we run it, it'll show you a prompt where you can type Ruby expressions one at a time, hitting Enter after each.
• IRB will immediately show you the result of each expression. You don't need to call puts or anything.

2.3.0 :001 > 1 + 2
 => 3
2.3.0 :002 > Time.now
 => 2017-09-02 13:31:38 -0700

• When you're done and you're ready to exit IRB, type exit and press Enter. You'll be returned to the system prompt.

2.3.0 :003 > exit
$ 

• IRB is a great way to try code out and see what it does, and even professional Ruby developers use it as a way to quickly test out ideas.

String Concatenation

So now that we know how irb works, let's use it to try out string concatenation.

$ irb
2.3.0 :001 > "a" + "b"
 => "ab"
2.3.0 :002 > "some words" + "more words"
 => "some wordsmore words"
2.3.0 :003 > "some words" + " " + "more words"
 => "some words more words"
2.3.0 :004 > myvar = "a string"
 => "a string"

• You can concatenate strings in variables

2.3.0 :005 > myvar + " abc"
 => "a string abc"

• Concatenation gives a new string, it doesn't change the string in the variable

2.3.0 :006 > myvar 
 => "a string"

• To change the variable's value, use an abbreviated assignment operator, which we'll talk more about soon

myva2.3.0 :007 > myvar += " abc"
 => "a string abc"
2.3.0 :008 > myvar
 => "a string abc"
myva2.3.0 :009 > myvar += " def"
 => "a string abc def"
myvar
2.3.0 :010 > myvar
 => "a string abc def"

• Strings can only be concatenated together with other strings. Anything else, like a number, will result in an error.
  • We'll be showing you a solution for this shortly.

2.3.0 :001 > 1 + "a string"
TypeError: String can't be coerced into Fixnum
        from (irb):1:in `+'
        from (irb):1
        from /Users/jay/.rvm/rubies/ruby-2.3.0/bin/irb:11:in `<main>'
2.3.0 :002 > "a string" + 1
TypeError: no implicit conversion of Fixnum into String
        from (irb):2:in `+'
        from (irb):2
        from /Users/jay/.rvm/rubies/ruby-2.3.0/bin/irb:11:in `<main>'

Updating the widget store

• Using string concatenation to fix our ask method
  • We need to print a space following the question we ask the user
  • We can do this using string concatenation

def ask(question)
  print question + " "
  gets
end

puts "Welcome to the widget store!"
answer = ask("How many widgets are you ordering?")

• Let's print what the user entered so they can confirm it's correct.

answer = ask("How many widgets are you ordering?")
puts "You entered" + answer + "widgets"

• Output:

You entered11
widgets

• Oops! We need to add spaces surrounding answer, so fix that: puts "You entered " + answer + " widgets"
  • Output:

You entered 11
 widgets

• You may be wondering why we didn't get an error, since strings can only be concatenated with other strings. The reason is, the value in the answer variable is a string. The gets method always returns strings. So even though the user entered a number, it's treated as a string. Eventually we'll have to convert it to an actual number, which we'll see how to do later.
• It still skips to a new line after printing answer. That's something we'll have to fix later as well.