if-else.cpp

#include <iostream>
using namespace std;

int main() {
    // =========================================================================
    // 1. COMPARISON OPERATORS (Used to compare two values)
    // =========================================================================
    // <   : Less than
    // <=  : Less than or equal to
    // >   : Greater than
    // >=  : Greater than or equal to
    // ==  : Equal to
    // !=  : Not equal to

    int time = 20;

    // =========================================================================
    // 2. BASIC IF...ELSE STATEMENT
    // =========================================================================
    // Checks a single condition. Runs 'if' block if true, otherwise 'else' block.
    if (time < 18) {
        cout << "Good day." << endl;
    } else {
        cout << "Good evening." << endl; // Output: Good evening.
    }

    // =========================================================================
    // 3. USING BOOLEAN VARIABLES IN CONDITIONS
    // =========================================================================
    // You can store conditions inside boolean variables (true/false) for clean code.
    bool isDay = time < 18; // Stores 'false' because 20 is not less than 18

    if (isDay) {
        cout << "Good day." << endl;
    } else {
        cout << "Good evening." << endl;
    }

    // =========================================================================
    // 4. IF...ELSE IF...ELSE LADDER
    // =========================================================================
    // Checks multiple conditions sequentially from top to bottom.
    int temp = 30;

    if (temp < 0) {
        cout << "It's freezing!\n";
    } else if (temp < 20) {
        cout << "It's cool.\n";
    } else {
        cout << "It's warm.\n"; // Output: It's warm.
    }

    // =========================================================================
    // 5. LOGICAL OPERATORS (AND, OR, NOT)
    // =========================================================================
    int a = 200, b = 33, c = 500;

    // AND (&&) : Returns true ONLY IF ALL conditions are true
    if (a > b && c > a) {
        cout << "Both conditions are true!\n";
    }

    // OR (||)  : Returns true IF AT LEAST ONE condition is true
    if (a > b || a > c) {
        cout << "At least one condition is true!\n";
    }

    // NOT (!)  : Reverses the boolean result (true -> false, false -> true)
    if (!(a < b)) {
        cout << "a is NOT less than b!\n";
    }

    // =========================================================================
    // 6. NESTED IF STATEMENTS
    // =========================================================================
    // Placing an 'if' statement inside another 'if' statement for secondary checks.
    int age = 20;
    bool isCitizen = true;

    if (age >= 18) {
        cout << "Old enough to vote.\n";
        
        // Inner check: executed only if the outer condition (age >= 18) is true
        if (isCitizen) {
            cout << "You are eligible to cast your vote.\n";
        } else {
            cout << "You must be a citizen to vote.\n";
        }
    } else {
        cout << "Not old enough to vote.\n";
    }

    // =========================================================================
    // 7. PRACTICAL EXAMPLE: CHECK EVEN OR ODD NUMBER
    // =========================================================================
    // The modulus operator (%) returns the remainder of division.
    int myNum = 5;

    if (myNum % 2 == 0) {
        cout << myNum << " is even.\n";
    } else {
        cout << myNum << " is odd.\n"; // Output: 5 is odd.
    }

    return 0;
}