if Statement in C++

An if statement allows a program to make a decision.

if (condition) {
    // code to execute
}

The code inside the braces executes only when the condition is true.

The basic syntax of an if statement is:

if (condition) {
    statement;
}

The condition is written inside parentheses, and the statements to execute are written inside curly braces.

int age = 20;

if (age >= 18) {
    std::cout << "You are an adult";
}

Because 20 is greater than or equal to 18, the message is displayed.

int number = 10;

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

The condition checks whether the number is greater than zero.

The equality operator == can be used inside an if condition.

int number = 10;

if (number == 10) {
    std::cout << "Number is 10";
}

The condition is true, so the message is displayed.

int number = 15;

if (number != 10) {
    std::cout << "Number is not 10";
}

Since 15 is not equal to 10, the condition is true.

int marks = 80;

if (marks > 50) {
    std::cout << "Good marks";
}

The statement executes because 80 is greater than 50.

int age = 15;

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

The condition is true because 15 is less than 18.

int marks = 40;

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

The condition is true because 40 is equal to the minimum required value.

int age = 18;

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

The condition is true because age is exactly 18.

An if block can contain multiple statements.

int marks = 80;

if (marks >= 40) {

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

}

Both statements execute when the condition is true.

Curly braces are recommended when writing the body of an if statement, especially when there is more than one statement.

if (marks >= 40) {
    std::cout << "Pass";
    std::cout << " Well done!";
}

A Boolean variable can be used directly as a condition.

bool isLoggedIn = true;

if (isLoggedIn) {
    std::cout << "Welcome";
}

The block executes because isLoggedIn is true.

Multiple conditions can be combined using the logical AND operator &&.

int age = 25;
bool hasID = true;

if (age >= 18 && hasID) {
    std::cout << "Allowed";
}

Both conditions must be true.

The logical OR operator || allows the block to execute when at least one condition is true.

int day = 6;

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

The logical NOT operator ! reverses a Boolean condition.

bool loggedIn = false;

if (!loggedIn) {
    std::cout << "Please log in";
}

Since loggedIn is false, !loggedIn is true.

#include <iostream>

int main() {

    int age;

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

    if (age >= 18) {
        std::cout << "You are an adult";
    }

    return 0;
}

The program displays the message only when the entered age is at least 18.

#include <iostream>

int main() {

    int number;

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

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

    return 0;
}

The modulus operator can be used inside an if condition to check whether a number is even.

int number = 20;

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

int marks;

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

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

The message is displayed when the marks are 40 or greater.

The AND operator can be used to check whether a value is inside a range.

int age = 25;

if (age >= 18 && age <= 60) {
    std::cout << "Age is within the range";
}

int a = 50;
int b = 30;

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

The condition compares the values of two variables.

#include <iostream>
#include <string>

int main() {

    std::string password = "admin123";

    if (password == "admin123") {
        std::cout << "Correct password";
    }

    return 0;
}

C++ std::string objects can be compared using the == operator.

An if statement can be placed inside another if statement. This is called a nested if.

int age = 25;
bool hasID = true;

if (age >= 18) {

    if (hasID) {
        std::cout << "Access allowed";
    }

}

char grade = 'A';

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

The condition compares the character with 'A'.

#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";
    }

    return 0;
}

The message is displayed only when both username and password match.

#include <iostream>

int main() {

    double amount;

    std::cout << "Enter purchase amount: ";
    std::cin >> amount;

    if (amount >= 1000) {
        std::cout << "You are eligible for a discount";
    }

    return 0;
}

The message appears when the purchase amount is at least 1000.

#include <iostream>

int main() {

    int marks;

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

    if (marks >= 40) {
        std::cout << "You passed the examination."
                  << std::endl;

        if (marks >= 75) {
            std::cout << "You scored a high mark.";
        }
    }

    return 0;
}

The second if statement is checked only when the first condition is true.

• Using = instead of == for comparison.
• Forgetting the parentheses around the condition.
• Forgetting curly braces when multiple statements belong to the if block.
• Writing an incorrect logical condition.
• Using a semicolon immediately after the if condition.
• Creating unnecessarily complicated nested conditions.
• Forgetting that an if statement executes only when its condition is true.

Example of a common mistake:

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

The semicolon ends the if statement. Avoid adding an unnecessary semicolon after the condition.

if (condition) {
    // statements
}