C++ If-Else-ElseIf Control Structure

In this tutorial, we’ll learn how the if, if-else, and if-else-if control structures work in C++. These are essential tools for decision making in any program.

1. The if Structure

The if control structure executes a block of code only when a specific condition is true. If the condition is false, the block is skipped entirely. It’s optional to have an else part.

Syntax:

if (condition) {
    // statements when condition is true
}

if (condition) {
    // statements when condition is true
}

Example:

#include <iostream>
using namespace std;

int main() {
    cout << "Please enter a number: ";
    int x;
    cin >> x;
    // Check if the number is negative
    if (x < 0) {
        cout << "Negative";
    }
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    cout << "Please enter a number: ";
    int x;
    cin >> x;
    // Check if the number is negative
    if (x < 0) {
        cout << "Negative";
    }
    return 0;
}

Explanation:

• The expression x < 0 is evaluated.
• If it’s true, cout << "Negative"; runs.
• If it’s false, nothing happens (the program continues).

2. The if-else Structure

When you want to handle both cases (true and false), you use if-else.

Syntax:

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

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

Example:

#include <iostream>
using namespace std;

int main() {
    cout << "Please enter a number: ";
    int x;
    cin >> x;
    if (x < 0) {
        cout << "Negative";
    } else {
        cout << "The number is not negative";
    }
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    cout << "Please enter a number: ";
    int x;
    cin >> x;
    if (x < 0) {
        cout << "Negative";
    } else {
        cout << "The number is not negative";
    }
    return 0;
}

Explanation:

• If x < 0 is true, it prints Negative.
• Otherwise (when x >= 0), it prints The number is not negative.

3. The if-else-if-else Structure

When you have multiple conditions to check sequentially, you use if-else-if. You can chain multiple else if blocks, and optionally a final else.

Syntax:

if (condition1) {
    // block1
} else if (condition2) {
    // block2
} else {
    // block when none of above conditions match
}

if (condition1) {
    // block1
} else if (condition2) {
    // block2
} else {
    // block when none of above conditions match
}

Example:

#include <iostream>
using namespace std;

int main() {
    cout << "Please enter a number: ";
    int x;
    cin >> x;

    if (x < 0) {
        cout << "Negative";
    } else if (x > 0) {
        cout << "Positive";
    } else {
        cout << "The number is 0";
    }

    return 0;
}

#include <iostream>
using namespace std;

int main() {
    cout << "Please enter a number: ";
    int x;
    cin >> x;

    if (x < 0) {
        cout << "Negative";
    } else if (x > 0) {
        cout << "Positive";
    } else {
        cout << "The number is 0";
    }

    return 0;
}

Explanation:

1. Checks x < 0. If true, prints Negative, and skips all further checks.
2. If not, checks x > 0. If true, prints Positive.
3. If neither is true (i.e. x == 0), executes the else block and prints The number is 0.

Tips & Best Practices

• Order matters: The conditions are evaluated top-to-bottom. Once one is true, the rest are ignored.
• Only one else: You can have many else if blocks, but at most one else at the end.
• Braces { } are safe: Even for a single statement, always using braces avoids confusion.
• Avoid deep nesting: If your logic is too nested, consider breaking it into functions or using early returns to make it cleaner.
• Don’t forget else when you want a fallback path.