C Logical Operators in Conditions

Logical Operators in Conditions

You can combine or reverse conditions using logical operators. These work together with if, else, and else if to build more complex decisions.

• && (AND) - all conditions must be true
• || (OR) - at least one condition must be true
• ! (NOT) - reverses a condition (true → false, false → true)

AND (&&)

Use AND (&&) when both conditions must be true:

int a = 200;
int b = 33;
int c = 500;

if (a > b && c > a) {
  printf("Both conditions are true\n");
}

OR (||)

Use OR (||) when at least one of the conditions can be true:

int a = 200;
int b = 33;
int c = 500;

if (a > b || a > c) {
  printf("At least one condition is true\n");
}

NOT (!)

The NOT operator (!) reverses a condition:

• If a condition is true, ! makes it false.
• If a condition is false, ! makes it true.

This is useful when you want to check that something is not the case:

int a = 33;
int b = 200;

if (!(a > b)) { 
  printf("a is NOT greater than b\n");
}

Real-Life Example

In real programs, logical operators are often used for access control. For example, to get access to a system, there are specific requirements:

You must be logged in, and then you either need to be an admin, or have a high security clearance (level 1 or 2):

bool isLoggedIn = true;
bool isAdmin = false;
int securityLevel = 3; // 1 = highest

if (isLoggedIn && (isAdmin || securityLevel <= 2)) {
  printf("Access granted\n");
} else {
  printf("Access denied\n");
}

// Try changing securityLevel and isAdmin to test different outcomes:
// securityLevel 1 = Access granted
// securityLevel 2 = Access granted
// securityLevel 3 = Access denied
// securityLevel 4 = Access denied
// If isAdmin = true, access is granted.

Visualize the Access Check

Choose a user below to see how C calculates the condition from the real-life example: