If...Else

Overview

If statements execute blocks of code conditionally based on a boolean expression. They form the backbone of decision-making in logic.

Syntax

cpp

int score = 85;

if (score >= 90) {
    cout << "Grade: A";
} else if (score >= 80) {
    // Nested if
    if (score == 85) {
        cout << "Grade: B (Solid)";
    } else {
        cout << "Grade: B";
    }
} else {
    cout << "Grade: C or lower";
}

Common Pitfalls

Forgetting braces `{}` for multi-line if blocks (only the first line is conditional without braces).
Using assignment `=` instead of equality `==`.

Interview Tips

Explain the concept of 'branch prediction' in modern CPUs and how highly unpredictable 'if' statements inside large loops can slow down performance.

Real-World Example

Validating user input boundaries.

example

cpp

#include <iostream>
using namespace std;

int main() {
    int age;
    cout << "Enter age: ";
    cin >> age;
    
    if (age < 0 || age > 120) {
        cout << "Invalid age.\n";
    } else if (age >= 18) {
        cout << "Access granted.\n";
    } else {
        cout << "Access denied.\n";
    }
    return 0;
}

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