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Functions (and later methods) are defined with def. Parameters are given, without types of course. Default values may be provided. Note that when we send an integer, the method does not change the value sent.
Ruby iterators are methods which take and run a block of code. The block can be delimited by curly braces or by the keywords do and end. The brackets have higher precedence, and variables declared in them are destroyed when the bracked code exits.
The ruby case statement is similar to the C/C++/Java switch, but more directly related to the similar (and superior) structures from Pascal and Ada. First, it assumes that each case ends where the next one starts, without needing a break to terminate a case. Secondly, each case can be expressed rather generally, with a single value, a range of value, or a list containing some of each.
The Ruby for loop is similar to the Python for or the perl foreach. Its basic operation is iterate over the contents of some collection. This may be an actual array or a range expression. A range expression is two numbers, surrounded by parens, and separated by either two dots or three. The three-dot form omits the last number from the range, while the two-dot version includes it. The three-dots version can be quite useful for creating a range of legal subscripts since the array size is not a legal subscript.
The while loop is conventional, but it also has a postfix form.
Following from the previous tutorial on Conditional Logic in Ruby, look at this example:
# Let the user guess.
print "Enter heads or tails? "
hort = gets.chomp
unless hort == 'heads' || hort == 'tails'
print "I _said_ heads or tails. Can't you read?\n"
exit(1)
end
# Now toss the coin.
toss = if rand(2) == 1 then
"heads"
else
"tails"
end
# Report.
print "Toss was ", toss, ".\n"
print "You Win!\n" if hort == toss
Some more amazing if lore:
unless keyword is like if, but uses the opposite sense of the test: The code is run if the test is false.if may look like a statement, but it is actually an expression, with a return value.if has a postfix form where the condition comes last. This works with unless as well.
This is the conventional use of the if in perl. Notice that there is no need for curly braces ({ and }). The body of the if ends with the appropriate keyword, end, else or elsif. The then word is generally optional, though you need it if you want to put start the body on the same line as the if, the way the last statement does.
The built-in gets function simply reads a line and returns it as a string. The chomp method from class String trims the line terminator. The prompts are generated with ordinary prints lacking a final newline.
# Get the parts of speech
print "Please enter a past-tense verb: "
verb = gets.chomp
print "Please enter a noun: "
noun = gets.chomp
print "Please enter a proper noun: "
prop_noun = gets.chomp
print "Please enter a an adverb: "
adv = gets.chomp
# Make the sentence.
print "#{prop_noun} got a #{noun} and\n#{verb} #{adv} around the block.\n"
Similarly, the to_f method of class String converts the input string to a floating-point number.
print "Triangle height: " h = gets.to_f; print "Triangle width: " w = gets.to_f; area = 0.5*h*w print "Triangle height ", h, " width ", w, " has area ", area, "\n"
Ruby generally uses line breaks instead of semicolons to separate statements. Lines can be continued by using a \ at the end, but this is rarely needed. If the line ends with pretty much anything that suggests there should be more, Ruby will continue on to the next line. This includes such things as ending with an operator, or inside parentheses or something else which needs to be closed.
Ruby arrays have operations similar to strings. As the quote notation creates a String object, the bracket notation creates an Array object.