Programming Crystal

Controlling the Flow

Now that you have a core set of variables, it’s time to drive decisions with them. As with any programming language, Crystal has a number of control flow constructs that let you specify the flow of program execution. We’ll go over some of them here, and we’ll add some more info in Chapter 3, ​Typing Variables and Controlling the Flow​.

Making Choices

Crystal offers the classic if expression with variations that let you create complex structures. A simple if expression tests a condition and does something if that condition is met:

foundations/control_flow.cr

hardness = 7  # quartz

if hardness < 8
   puts "softer than topaz"
end
# => softer than topaz

In this case, 7 is less than 8, so Crystal will report “softer ...