What is and how to use the IF-ELSE conditional in C++

The if and if-else conditionals are fundamental control structures in C++ that allow making decisions based on boolean evaluations (true or false).

The IF Conditional

The if structure evaluates a boolean expression and executes a block of code only if the expression evaluates to true. The basic syntax of an if conditional in C++ is:

if (condition) {
    // Code to execute if the condition is true
}

Let’s see it with an example:

int number = 10;

if (number > 5) {
    std::cout << "The number is greater than 5" << std::endl;
}

The IF ELSE Conditional

The if conditional allows adding an else block of alternative code that will execute if the if condition is false. The basic syntax is:

if (condition) {
    // Code to execute if the condition is true
} else {
    // Code to execute if the condition is false
}

Let’s see it with an example:

int number = 3;

if (number > 5) {
    std::cout << "The number is greater than 5" << std::endl;
} else {
    std::cout << "The number is not greater than 5" << std::endl;
}

The IF ELSE-IF Conditional

To evaluate multiple conditions, multiple if / else-if / else blocks can be chained. This allows evaluating several conditions in sequence until one of them is true.

if (condition1) {
    // Code to execute if condition1 is true
} else if (condition2) {
    // Code to execute if condition1 is false and condition2 is true
} else {
    // Code to execute if all previous conditions are false
}

Nested Conditionals

It is possible to nest multiple if and if-else structures to evaluate more complex conditions.

int number = 0;
if (number > 0) {
    std::cout << "The number is positive." << std::endl;
} else {
    if (number < 0) {
        std::cout << "The number is negative." << std::endl;
    } else {
        std::cout << "The number is zero." << std::endl;
    }
}

Using Logical Operators in Conditionals

To evaluate multiple conditions within a single if, logical operators such as && (logical AND) and || (logical OR) can be used.

For example, the && operator evaluates to true only if both conditions are true.

int number = 10;

if (number > 5 && number < 15) {
    std::cout << "The number is between 5 and 15" << std::endl;
}

While the || operator evaluates to true if at least one of the conditions is true.

int number = 20;

if (number < 5 || number > 15) {
    std::cout << "The number is less than 5 or greater than 15" << std::endl;
}

Practical Examples

int number = 10;

if (number > 15) {
    std::cout << "The number is greater than 15" << std::endl;
} else if (number > 5) {
    std::cout << "The number is greater than 5 but less than or equal to 15" << std::endl;
} else {
    std::cout << "The number is 5 or less" << std::endl;
}

int a = 5, b = 10, c = 3;
int largest;

if (a > b && a > c) {
    largest = a;
} else if (b > a && b > c) {
    largest = b;
} else {
    largest = c;
}

std::cout << "The largest number is: " << largest << std::endl;

int grade = 85;
std::string range;

if (grade >= 90) {
    range = "A";
} else if (grade >= 80) {
    range = "B";
} else if (grade >= 70) {
    range = "C";
} else if (grade >= 60) {
    range = "D";
} else {
    range = "F";
}

std::cout << "The grade is: " << range << std::endl;