It gives you the choice of calculating the area of a circle, rectangle, or triangle:

Code:
#!/usr/bin/env ruby

# The Area Calculator
# Calculate the area of a variety of shapes

def circle()
 # Get radius
 print "Radius: "
 radius = STDIN.gets
 radius = Float(radius.chop!)

 # Calculate area and print it
 area = 3.14 * radius * radius
 print "The area is ", area, "\n"
 exit
end

def rectangle()
 # Get base and height
 print "Base: "
 base = STDIN.gets
 base = Float(base.chop!)
 print "Height: "
 height = STDIN.gets
 height = Float(height.chop!)

 # Calculate area and print it
 area = base * height
 print "The area is ", area, "\n"
 exit
end

def triangle()
 # Get base and height
 print "Base: "
 base = STDIN.gets
 base = Float(base.chop!)
 print "Height: "
 height = STDIN.gets
 height = Float(height.chop!)

 # Calculate the area and print it
 area = (base * height) / 2
 print "The area is ", area, "\n"
 exit
end

# Start the script

print "Area Calculator!\n\n"
print "Select a shape:\n"
print "1 Circle\n"
print "2 Rectangle\n"
print "3 Triangle\n\n"
print "? "

# Get input - Which shape?
choice = STDIN.gets
# Catch exceptions when input is String or Float - exit
begin
 choice = Integer(choice.chop!)
rescue
 print "Invalid selection\n"
 exit
end

print "\n"

# Calculate the area of the selection
# Catch exceptions when input in area calculations
# is String
begin
 case choice
  when 1
   circle()
  when 2
   rectangle()
  when 3
   triangle()
 end
rescue
end

# This is reached when an exception occurs above
# or when choice does not equal 1, 2, or 3
# Otherwise, the shape functions exit after area calculation
print "Invalid Selection\n"
What do you think? A little sloppy? Should I add more shapes?

By the way, is there a default statement in Ruby (for the case statement)? And does anyone know of any good Ruby tutorials? I found like two of them, and they aren't very... super.