Variables in Crystal

In Crystal, variables are explicitly declared and used by the compiler to check type-correctness of function calls.

# Variables are declared using the `=` operator

a = "initial"
puts a

# You can declare multiple variables at once
b, c = 1, 2
puts "#{b} #{c}"

# Crystal will infer the type of initialized variables
d = true
puts d

# Variables declared without a corresponding
# initialization are given their type's default value.
# For example, the default value for Int32 is 0.
e = 0
puts e

# In Crystal, there's no special syntax for short 
# declaration. The `=` operator is used for both 
# declaration and assignment.
f = "apple"
puts f

To run the program, save it as variables.cr and use the crystal command:

$ crystal variables.cr
initial
1 2
true
0
apple

Let’s break down the key points:

1. In Crystal, you don’t need to explicitly declare variable types. The type is inferred from the assigned value.

2. Multiple variable assignment is supported, as shown with b, c = 1, 2.

3. Crystal doesn’t have a separate keyword for variable declaration. The = operator is used for both declaration and assignment.

4. Variables are automatically initialized with a default value if not explicitly assigned. For integers, this is 0.

5. Crystal doesn’t have a special short declaration syntax like :=. The = operator is used consistently.

6. String interpolation is done using #{...} within string literals.

Crystal’s syntax is designed to be clean and expressive, making it easy to declare and work with variables in your programs.