if-else Statement in C++

 

The if-else statement in C++ is used for decision-making. It allows the program to execute one block of code if a condition is true and another block if the condition is false.

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1️⃣ Basic if-else Statement

#include <iostream>
using namespace std;

int main() {
    int num;
    cout << "Enter a number: ";
    cin >> num;

    if (num > 0) {
        cout << "The number is positive." << endl;
    } else {
        cout << "The number is not positive." << endl;
    }

    return 0;
}

Output:

Enter a number: 5
The number is positive.

📌 If num is negative or zero, it will print "The number is not positive.".

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2️⃣ if-else with Even/Odd Check

#include <iostream>
using namespace std;

int main() {
    int num;
    cout << "Enter a number: ";
    cin >> num;

    if (num % 2 == 0) {
        cout << "The number is even." << endl;
    } else {
        cout << "The number is odd." << endl;
    }

    return 0;
}

Output:

Enter a number: 7
The number is odd.

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3️⃣ if-else with Multiple Conditions (if-else if-else)

If there are multiple conditions, we use if-else if-else.

#include <iostream>
using namespace std;

int main() {
    int marks;
    cout << "Enter your marks: ";
    cin >> marks;

    if (marks >= 90) {
        cout << "Grade: A" << endl;
    } else if (marks >= 75) {
        cout << "Grade: B" << endl;
    } else if (marks >= 50) {
        cout << "Grade: C" << endl;
    } else {
        cout << "Grade: F (Fail)" << endl;
    }

    return 0;
}

Output:

Enter your marks: 80
Grade: B

📌 The conditions are checked in order, and the first matching condition executes.

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4️⃣ Nested if-else

You can place an if statement inside another if statement, called nested if.

#include <iostream>
using namespace std;

int main() {
    int age;
    cout << "Enter your age: ";
    cin >> age;

    if (age >= 18) {
        if (age >= 60) {
            cout << "You are a senior citizen." << endl;
        } else {
            cout << "You are an adult." << endl;
        }
    } else {
        cout << "You are a minor." << endl;
    }

    return 0;
}

Output:

Enter your age: 65
You are a senior citizen.

📌 Inner if executes only if the outer if condition is true.

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5️⃣ Using Logical Operators (&&, ||, !)

Example: Checking Voting Eligibility

#include <iostream>
using namespace std;

int main() {
    int age;
    cout << "Enter your age: ";
    cin >> age;

    if (age >= 18 && age <= 60) {  // Both conditions must be true
        cout << "You are eligible to work." << endl;
    } else {
        cout << "You are either too young or retired." << endl;
    }

    return 0;
}

Output:

Enter your age: 25
You are eligible to work.

📌 && ensures both conditions are true before executing the if block.

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6️⃣ Using Ternary Operator (? :)

A compact alternative to if-else:

#include <iostream>
using namespace std;

int main() {
    int num;
    cout << "Enter a number: ";
    cin >> num;

    string result = (num % 2 == 0) ? "Even" : "Odd";  // Ternary operator
    cout << "The number is " << result << "." << endl;

    return 0;
}

Output:

Enter a number: 9
The number is Odd.

📌 ? is a shorthand for if-else when assigning values based on a condition.

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Conclusion

• Use if when checking a single condition.
• Use if-else for two-way decision making.
• Use if-else if-else for multiple conditions.
• Use nested if for hierarchical decision-making.
• Use logical operators (&&, ||, !) for complex conditions.
• Use ternary operator (? :) for short if-else statements.

Would you like to see an example of error handling (e.g., invalid input handling)? 🚀