Blocks and Scopes

Block scope

A block is { ... }. A name declared inside a block exists from its declaration to that block's closing brace:

int main(void) {
    int x = 1;            // visible to the end of main
    {
        int y = 2;        // visible inside these braces only
        x = x + y;
    }
    // y does not exist here
    return x;             // 3
}

Loop and if bodies are blocks too — the classic bug:

for (int i = 0; i < 3; i++) { }   // i exists only in the loop
// i++ here is an error

Shadowing

An inner declaration with the same name hides the outer one:

int total = 100;
{
    int total = 5;        // a DIFFERENT variable
    printf("%d\n", total); // 5
}
printf("%d\n", total);    // 100 — untouched

Shadowing is legal but confusing. Avoid reusing names in nested scopes.