Rustlings Topic: Variables

In Rust, variables are immutable by default. When a variable is immutable, once a value is bound to a name, you can’t change that value. You can make them mutable by adding mut in front of the variable name.

This is the first topic of the rustlings. And there is nothing really special about it.
Exercises are just checking whether you are familiar with the basic syntaxes of the Rust.
If you find any of the exercises a bit confusing, please re-read The Book and/or Rust By Example.

You may find solution code for the topic from my repo.