C++Logical OperatorsLogical OR

Logical OR (||) Operator in C++

The Logical OR operator (||) in C++ is used to evaluate two or more conditions, and it returns true if at least one of the conditions is true.

It is frequently used in decision-making constructs like if, while, and for when only one condition needs to be satisfied to proceed.

How the Logical OR Works

Syntax:

condition1 || condition2

This expression returns:

  • true if either condition1 or condition2 is true.
  • false only if both are false.

Truth Table

condition1condition2condition1 || condition2
truetruetrue
truefalsetrue
falsetruetrue
falsefalsefalse

Short-Circuit Behavior

In the expression A || B:

  • If A is true, B is not evaluated. This is called short-circuit evaluation and is used for efficiency and safety.

Example 1: Basic Integer Conditions

or_basic_integers.cpp
int a = 10, b = 5;
std::cout << (a > 8 || b > 10);

Explanation

  • a > 8 → true
  • b > 10 → false
  • true || false → true

Output: 1

Example 2: Both Conditions False

or_both_false.cpp
int x = 3, y = 1;
std::cout << (x > 10 || y > 5);

Explanation

  • Both conditions are false
  • false || false → false

Output: 0

Example 3: In an if Statement

or_if_statement.cpp
int age = 17;
bool hasPermission = true;
 
if (age >= 18 || hasPermission) {
    std::cout << "Access granted.";
}

Explanation

  • First condition: false
  • Second condition: true
  • At least one is true → Access granted.

Example 4: Short-Circuiting Safety

or_short_circuit.cpp
int a = 10;
 
if (a > 0 || (10 / a) > 1) {
    std::cout << "Safe expression.";
}

Explanation

  • a > 0 → true
  • Because the first condition is true, second (10 / a) is not evaluated.
  • This prevents unnecessary or unsafe operations.

Example 5: With Boolean Variables

or_booleans.cpp
bool x = false, y = true;
 
std::cout << (x || y);  // Output: 1

Explanation

  • false || true → true → Output: 1

Example 6: With Character Comparison

or_characters.cpp
char grade = 'D';
 
std::cout << (grade == 'A' || grade == 'B');  // Output: 0

Explanation

  • Both comparisons are false → false || false → false → Output: 0

Example 7: With Strings

or_strings.cpp
std::string input = "guest";
 
if (input == "admin" || input == "guest") {
    std::cout << "Welcome!";
}

Explanation

  • Second condition is true → Access granted.

Example 8: Acceptable Range OR Check

or_range_check.cpp
int temp = -5;
 
std::cout << (temp < 0 || temp > 100);  // Output: 1

Explanation

  • One of the conditions is true → Result is true

Example 9: Use in Loop (Not common but possible)

or_loop_example.cpp
int attempts = 1;
bool adminOverride = true;
 
while (attempts <= 3 || adminOverride) {
    std::cout << "Trying...\n";
    break;
}

Explanation

  • Even if attempts exceed limit, adminOverride allows access

Key Takeaways

  • Use || when only one condition needs to be true.
  • Short-circuit evaluation ensures that the second condition is only evaluated if necessary.
  • It is ideal for writing flexible, fault-tolerant decision logic.
  • Works seamlessly with integers, characters, booleans, and even strings.
Logical ANDLogical NOT