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Logical Operators

Logical operators let you combine multiple conditions in C. There are three main logical operators you'll use all the time:

&& – Logical AND: true if both conditions are true
|| – Logical OR: true if either condition is true
! – Logical NOT: inverts a boolean value

int age = 25;
bool has_license = true;

if (age >= 18 && has_license) {
    printf("Can drive\n");
}

Short-Circuit Evaluation

C uses short-circuit evaluation with logical operators. This means:

With &&, if the first condition is false, the second isn't even checked (because the whole thing is already false)
With ||, if the first condition is true, the second isn't checked (because the whole thing is already true)

if (x != 0 && 10 / x > 2) {
    // The division only happens if x != 0
    // This prevents a division by zero error
    printf("Safe!\n");
}

Operator Precedence

Logical NOT (!) has higher precedence than AND (&&), which has higher precedence than OR (||). When in doubt, use parentheses to make your intent crystal clear:

// without parentheses – might be confusing
if (!is_raining && is_sunny || is_weekend)

// with parentheses – much clearer
if ((!is_raining && is_sunny) || is_weekend)

Assignment

The Sneklang package manager needs an access control system for its private package registry. Take a look at exercise.h and implement the function in exercise.c.

The can_access_registry function should return 1 (true) if a user can access the private registry, or 0 (false) if they cannot.

A user can access the private registry if any of these conditions are met:

They have is_premium set to 1 (true)
They have both reputation >= 100 AND has_2fa (two-factor authentication) set to 1 (true)

In C, we use 1 for true and 0 for false when returning boolean-like values from functions that return int.