Control Flow in C++: Conditionals (if, else, else if)

What You’ll Learn

By the end of this post, you’ll be able to:

• Make decisions in code using if, else, and else if
• Use relational and logical operators
• Handle multiple conditions
• Write clean, readable conditional logic

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Why Use Conditionals?

Not all programs follow a single path. Often, you want your program to make decisions based on user input or current values.

For example:

• If the user is logged in, show their dashboard.
• If the number is negative, print an error.
• If the temperature is high, turn on a fan.

C++ gives you conditionals to handle such cases.

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The if Statement

The if statement runs a block of code only if a condition is true.

Syntax:

if (condition) {
    // code runs if condition is true
}

Example:

int number = 10;

if (number > 0) {
    cout << "The number is positive." << endl;
}

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The else Statement

The else block runs when the if condition is false.

int number = -5;

if (number > 0) {
    cout << "Positive number." << endl;
} else {
    cout << "Not a positive number." << endl;
}

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The else if Ladder

Use else if to check multiple conditions in order.

int score = 85;

if (score >= 90) {
    cout << "Grade: A" << endl;
} else if (score >= 80) {
    cout << "Grade: B" << endl;
} else if (score >= 70) {
    cout << "Grade: C" << endl;
} else {
    cout << "Grade: F" << endl;
}

Conditions are checked from top to bottom. The first one that is true gets executed; others are skipped.

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Relational Operators

These operators compare two values:

Operator	Meaning	Example (x = 5, y = 10)
==	Equal to	x == y → false
!=	Not equal to	x != y → true
>	Greater than	x > y → false
<	Less than	x < y → true
>=	Greater than or equal	x >= y → false
<=	Less than or equal	x <= y → true

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Logical Operators

Used to combine multiple conditions.

Operator	Meaning	Example
&&	Logical AND	(x > 0 && x < 10) → true if both are true
`		`
!	Logical NOT	!(x == y) → true if x != y

Example:

int age = 25;
bool hasLicense = true;

if (age >= 18 && hasLicense) {
    cout << "You can drive." << endl;
} else {
    cout << "You cannot drive." << endl;
}

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Nested if Statements

You can put one if inside another. Be careful with indentation and logic.

int number = 8;

if (number > 0) {
    if (number % 2 == 0) {
        cout << "Positive even number." << endl;
    } else {
        cout << "Positive odd number." << endl;
    }
}

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Example: Simple Login Check

#include <iostream>
#include <string>
using namespace std;

int main() {
    string username;
    string password;

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

    if (username == "admin" && password == "1234") {
        cout << "Login successful!" << endl;
    } else {
        cout << "Invalid credentials." << endl;
    }

    return 0;
}

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Common Mistakes to Avoid

• Using = instead of == in conditions
  • if (x = 5) assigns 5 to x, which is almost always a bug
• Forgetting braces {} for multiple statements
• Writing conditions that always evaluate the same way (like if (true))

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Mini Exercises

1. Write a program that checks if a number is even or odd.
2. Ask the user for their age, and print:
   • “Child” if age < 13
   • “Teenager” if age between 13 and 19
   • “Adult” if age >= 20
3. Input 3 numbers and find the largest using if/else if.

Try these before looking up solutions.

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Summary

In this post, you learned how to:

• Use if, else, and else if to make decisions
• Work with comparison and logical operators
• Combine multiple conditions
• Write programs that respond to different inputs

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Coming Up Next

In the next post, we’ll dive into Loops and Iteration — making your programs repeat tasks using while, for, and do-while.