Summary

Variables in Rust are, by default, immutable. Immutable variables can be shadowed, but never changed.

You can make a variable mutable with the mut keyword in its let statement.

Once mutable, you can change the value of a variable with assignment (e.g., x = 5;) and mutation operators (e.g., x += 2;).

Mutation is almost always necessary to perform iteration.

A while expression is like an if expression, but continues to evaluate the body as long as the condition remains true.

You can nest loops inside each other to create more powerful loops.

You can use let to declare variables without assigning, though you probably don’t want to.