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Ruby Programming
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Control Structures

Ruby has all the usual control structures, such as if statements and while loops. Java, C, and Perl programmers may well get caught by the lack of braces around the bodies of these statements. Instead, Ruby uses the keyword end to signify the end of a body.

if count > 10
  puts "Try again"
elsif tries == 3
  puts "You lose"
  puts "Enter a number"

Similarly, while statements are terminated with end.

while weight < 100 and numPallets <= 30
  pallet = nextPallet()
  weight += pallet.weight
  numPallets += 1

Ruby statement modifiers are a useful shortcut if the body of an if or while statement is just a single expression. Simply write the expression, followed by if or while and the condition. For example, here's a simple if statement.

if radiation > 3000
  puts "Danger, Will Robinson"

Here it is again, rewritten using a statement modifier.

puts "Danger, Will Robinson" if radiation > 3000

Similarly, a while loop such as

while square < 1000
   square = square*square

becomes the more concise

square = square*square  while square < 1000

These statement modifiers should seem familiar to Perl programmers.
Ruby Programming
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