Scope

Overview

Scope determines where a variable is accessible and how long it lives. Local variables die when the block ends. Global variables live for the entire program. Static local variables live for the entire program but are only accessible in their local block.

Syntax

cpp

int globalVar = 10; // Accessible anywhere

void counter() {
    int localVar = 0;        // Recreated every call
    static int statVar = 0;  // Created once, persists across calls
    
    localVar++;
    statVar++;
}

Common Pitfalls

Shadowing: Declaring a local variable with the exact same name as a global variable, which hides the global one.
Overusing global variables makes code hard to test, debug, and trace.

Interview Tips

Be able to explain exactly what `static` does inside a function. It changes the lifetime from 'automatic' (stack) to 'static' (data segment), meaning it retains its value between function calls.

Real-World Example

Using static variables to track how many times a function is called.

example

cpp

#include <iostream>
using namespace std;

void generateID() {
    static int currentID = 1000; // Only runs the first time
    currentID++;
    cout << "Generated ID: " << currentID << endl;
}

int main() {
    generateID(); // 1001
    generateID(); // 1002
    generateID(); // 1003
    return 0;
}

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