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Ruby Constants

A constant is a name written in capital letters. A constant is meant to hold one value that stays fixed.

A constant holds a value

LIMIT is written in capital letters. The puts line prints the value stored in it.

LIMIT = 100
puts LIMIT

One value changes, one stays

The variable count changes between the prints. LIMIT prints the same value both times.

LIMIT = 10
count = 1
puts LIMIT
puts count
count = 2
puts LIMIT
puts count

Changing a constant warns

The second line stores a new value in LIMIT. Ruby prints a warning, and the program prints no value here.

LIMIT = 5
LIMIT = 9

Example

MAX_SCORE = 100
score = 80
puts MAX_SCORE
puts score
score = 90
puts score

Key points

  • A constant is a name meant to stay fixed.
  • A constant name starts with a capital letter.
  • Constant names in this course use capital letters for the whole name.
  • Use = to store a value in a constant.
  • Storing a new value in a constant prints a warning.
  • The value still changes after the warning.

In this example, MAX_SCORE holds 100. score holds 80, and the next line prints it. score then holds 90, and the last line prints 90.

Note

A warning is not an error, and the program still runs.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz Ruby Compiler

Exercise

Which line stores the number 100 in a constant named LIMIT?