Lesson 169 +10 XP

Static Local Variables

Normally a local variable is created each call and destroyed at the end. A static local is different: it keeps its value between calls.

The magic keyword

Add static to a local declaration:

int nextId() {
    static int id = 0;   // created once, keeps its value
    id = id + 1;
    return id;
}

Each call to nextId returns a bigger number: 1, 2, 3, ... The variable id is initialized only once - the first time the function runs - and then survives for the rest of the program.

How it differs from a normal local

void counter() {
    int normal = 0;       // reset to 0 on every call
    static int keep = 0;  // initialized once, then kept

    normal = normal + 1;
    keep = keep + 1;
    cout << normal << " " << keep << endl;
}

Every call prints 1 for normal, but keep grows: 1, 2, 3, ...

When to use static locals

Counting across calls: total invocations, running IDs, cached values.
Lazy initialization: a resource (like a big table) built the first time it's needed and reused after.
Simple, single-instance state that shouldn't be a global.

int getCount() {
    static int count = 0;
    count = count + 1;
    return count;
}

Keep it simple

Static locals are handy but easy to overuse. They make a function stateful: calling it twice can give different results. Use them when the state is genuinely meant to persist - not just to avoid a global.

TL;DR

static int count = 0; inside a function is created once.
It keeps its value between calls; count = 0 runs only the first time.
Great for counters, IDs, and lazily built one-time resources.
The initializer runs on the first call, not on every call.
Don't overuse them - they make functions stateful.

Static Local Variables