if-else Statement in C++

The if-else statement allows a program to execute one block when a condition is true and another block when the condition is false.

if (condition) {
    // code when condition is true
}
else {
    // code when condition is false
}

The basic syntax of an if-else statement is:

if (condition) {
    statement1;
}
else {
    statement2;
}

Only one of the two blocks executes.

int age = 20;

if (age >= 18) {
    std::cout << "Adult";
}
else {
    std::cout << "Minor";
}

Since the age is 20, the condition is true and Adult is displayed.

The program first checks the condition.

1. If the condition is true, the if block executes.
2. If the condition is false, the else block executes.
3. Only one block is executed.

if (condition) {
    // True
}
else {
    // False
}

int marks = 35;

if (marks >= 40) {
    std::cout << "Pass";
}
else {
    std::cout << "Fail";
}

Because 35 is less than 40, the output is Fail.

The modulus operator % can be used to check whether a number is even or odd.

int number = 7;

if (number % 2 == 0) {
    std::cout << "Even";
}
else {
    std::cout << "Odd";
}

int number = -10;

if (number >= 0) {
    std::cout << "Positive";
}
else {
    std::cout << "Negative";
}

Since -10 is not greater than or equal to zero, the else block executes.

#include <iostream>

int main() {

    int age;

    std::cout << "Enter your age: ";
    std::cin >> age;

    if (age >= 18) {
        std::cout << "You can vote";
    }
    else {
        std::cout << "You cannot vote";
    }

    return 0;
}

int a = 50;
int b = 30;

if (a > b) {
    std::cout << "A is greater";
}
else {
    std::cout << "B is greater or equal";
}

The condition compares the values of a and b.

int a = 10;
int b = 10;

if (a == b) {
    std::cout << "Both are equal";
}
else {
    std::cout << "They are different";
}

int marks = 80;

if (marks > 50) {
    std::cout << "Marks are greater than 50";
}
else {
    std::cout << "Marks are 50 or less";
}

int age = 15;

if (age < 18) {
    std::cout << "Minor";
}
else {
    std::cout << "Adult";
}

int marks = 40;

if (marks >= 40) {
    std::cout << "Pass";
}
else {
    std::cout << "Fail";
}

The condition includes 40 because the operator is >=.

int age = 18;

if (age <= 18) {
    std::cout << "Age is 18 or below";
}
else {
    std::cout << "Age is above 18";
}

bool loggedIn = true;

if (loggedIn) {
    std::cout << "Welcome";
}
else {
    std::cout << "Please login";
}

If the Boolean value is true, the if block executes. Otherwise, the else block executes.

The && operator can combine two conditions.

int age = 25;
bool hasID = true;

if (age >= 18 && hasID) {
    std::cout << "Entry allowed";
}
else {
    std::cout << "Entry denied";
}

Both conditions must be true for the if block to execute.

The || operator is used when at least one condition can be true.

int day = 6;

if (day == 6 || day == 7) {
    std::cout << "Weekend";
}
else {
    std::cout << "Working day";
}

#include <iostream>
#include <string>

int main() {

    std::string password;

    std::cout << "Enter password: ";
    std::cin >> password;

    if (password == "1234") {
        std::cout << "Correct password";
    }
    else {
        std::cout << "Incorrect password";
    }

    return 0;
}

char grade = 'A';

if (grade == 'A') {
    std::cout << "Excellent";
}
else {
    std::cout << "Other grade";
}

Characters are written inside single quotes.

#include <iostream>
#include <string>

int main() {

    std::string name = "Rahul";

    if (name == "Rahul") {
        std::cout << "Hello Rahul";
    }
    else {
        std::cout << "Unknown user";
    }

    return 0;
}

Both the if and else blocks can contain multiple statements.

int marks = 75;

if (marks >= 40) {

    std::cout << "Result: Pass" << std::endl;
    std::cout << "Congratulations!";

}
else {

    std::cout << "Result: Fail" << std::endl;
    std::cout << "Try again.";

}

double amount = 1500;

if (amount >= 1000) {
    std::cout << "Discount available";
}
else {
    std::cout << "No discount";
}

The customer gets the message for a discount when the amount is at least 1000.

#include <iostream>

int main() {

    int age;

    std::cout << "Enter age: ";
    std::cin >> age;

    if (age >= 18) {
        std::cout << "Eligible";
    }
    else {
        std::cout << "Not eligible";
    }

    return 0;
}

#include <iostream>
#include <string>

int main() {

    std::string username;
    std::string password;

    std::cout << "Username: ";
    std::cin >> username;

    std::cout << "Password: ";
    std::cin >> password;

    if (username == "admin" && password == "1234") {
        std::cout << "Login successful";
    }
    else {
        std::cout << "Invalid login details";
    }

    return 0;
}

An if statement can contain another if statement.

int age = 25;
bool hasID = true;

if (age >= 18) {

    if (hasID) {
        std::cout << "Entry allowed";
    }
    else {
        std::cout << "ID required";
    }

}
else {

    std::cout << "You are underage";

}

#include <iostream>

int main() {

    int number;

    std::cout << "Enter number: ";
    std::cin >> number;

    if (number >= 0) {
        std::cout << "Positive or zero";
    }
    else {
        std::cout << "Negative";
    }

    return 0;
}

#include <iostream>

int main() {

    int marks;

    std::cout << "Enter marks: ";
    std::cin >> marks;

    if (marks >= 40) {

        std::cout << "Pass" << std::endl;

        if (marks >= 75) {
            std::cout << "Good performance";
        }

    }
    else {

        std::cout << "Fail" << std::endl;
        std::cout << "Work harder";

    }

    return 0;
}

For simple two-choice assignments, C++ also provides the conditional or ternary operator. However, a normal if-else statement is often easier for beginners to read.

int age = 20;

if (age >= 18) {
    std::cout << "Adult";
}
else {
    std::cout << "Minor";
}

The above logic can also be written using a ternary operator, but understanding if-else first is important.

• Using = instead of == for comparison.
• Forgetting parentheses around the condition.
• Putting an unnecessary semicolon after the if condition.
• Forgetting curly braces when multiple statements are required.
• Writing else without a corresponding if.
• Using incorrect logical operators.
• Writing conditions that do not represent the intended logic.

Incorrect:

if (marks >= 40); {
    std::cout << "Pass";
}
else {
    std::cout << "Fail";
}

Avoid the unnecessary semicolon after the if condition.

if (condition) {
    // true block
}
else {
    // false block
}