global vs local variables

Topics

• programming basics
• memory management
• competitive programming

int score = 50;
int main() {
    int score = 100;
    cout << "Local variable is " << score << '\n';
    cout << "Global variable is " << ::score << '\n';
    return 0;
}

• Global: Variables declared outside functions; stored in data segment
• Local: Variables declared inside functions; stored on stack

Warning

• Use globals for large arrays in competitive programming, as opposed to declaring inside functions, since stack size is typically 1-8 MB in competitions
• Globals initialized to 0/null, locals have garbage values
• Thread safety concerns with globals

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