可変状態にはvarを使う

Some values truly need to move: a counter, a running total, a current score. For those, Zig gives you the var keyword.

The keyword var creates a mutable binding. Unlike const, the name you declare with var can be reassigned again and again.

Once a value is a var, updating it is just a plain assignment. No special syntax is needed, only the name and a new value.

You can compute a new value from the old one. Adding to a counter is the classic example of useful mutation in a loop.

For a var that starts at zero, Zig may ask for a type so it knows the integer width. Annotate it once and you are set.

If you declare a var but never actually change it, Zig warns you. It nudges you to use const instead for a clearer intent.

Mutable locals live inside functions and last for that scope. A loop accumulator declared with var is a perfect everyday use.

Every var is one more thing that can change underfoot. Use it where change is the point, not as a lazy default choice.

A while loop often drives a var forward each pass. The binding updates, the condition rechecks, and the loop advances.

A var can change its value but never its type. An i32 stays an i32; you cannot suddenly store text in a number binding.

Think of it simply: const is a value pinned in place, while var is a value that is meant to move. Reach for var only when it must.

You need a counter that increases inside a loop. Which keyword should declare it?

You learned that var creates a mutable binding for values that change. Annotate its type when needed, and use it only where mutation is truly the goal. 🔁