C++ Loops

Key Loop Concepts

for (int i = 0; i < 5; i++) {
    // code here
}

while (condition) {
    // code here
}

do {
    // code here
} while (condition);

break;    // exit loop
continue; // skip iteration

🔹 For Loop

A for loop repeats a block of code a specific number of times, making it ideal for iterating over sequences. It consists of an initialization, a condition, and an increment/decrement expression. In the multiplication example, the loop runs from 1 to 10, calculating and displaying each product with 3. This structured iteration is efficient for tasks where the exact number of repetitions is known beforehand, such as processing arrays or generating tables.

#include <iostream>
using namespace std;

int main() {
    // Print multiplication table of 3
    cout << "Multiplication table of 3:" << endl;
    
    for (int i = 1; i <= 10; i++) {
        cout << "3 x " << i << " = " << (3 * i) << endl;
    }
    
    return 0;
}

🔹 While Loop

A while loop executes repeatedly as long as a specified condition remains true, perfect for uncertain iteration counts. It checks the condition before each iteration. In the provided example, numbers are added sequentially until the cumulative sum exceeds 50, demonstrating its use in scenarios like reading data until a sentinel value or achieving a target threshold where the total iterations aren't predetermined.

#include <iostream>
using namespace std;

int main() {
    int number = 1;
    int sum = 0;
    
    cout << "Adding numbers until sum exceeds 50:" << endl;
    
    while (sum <= 50) {
        sum += number;
        cout << "Added " << number << ", sum = " << sum << endl;
        number++;
    }
    
    cout << "Final sum: " << sum << endl;
    
    return 0;
}

🔹 Do-While Loop

The do-while loop guarantees at least one execution by evaluating the condition after the loop body. This is crucial for menu-driven programs or input validation where an action must occur before checking for exit criteria. The sample menu prompts the user for a choice (1-3) and continues to display options until the user selects "Exit," ensuring the interface is presented initially regardless of the condition state.

#include <iostream>
using namespace std;

int main() {
    int choice;
    
    do {
        cout << "\n--- Simple Menu ---" << endl;
        cout << "1. Say Hello" << endl;
        cout << "2. Say Goodbye" << endl;
        cout << "3. Exit" << endl;
        cout << "Enter choice (1-3): ";
        cin >> choice;
        
        switch (choice) {
            case 1:
                cout << "Hello there!" << endl;
                break;
            case 2:
                cout << "Goodbye!" << endl;
                break;
            case 3:
                cout << "Exiting..." << endl;
                break;
            default:
                cout << "Invalid choice!" << endl;
        }
    } while (choice != 3);
    
    return 0;
}

🔹 Loop Control Statements

The break and continue statements provide precise control over loop execution flow. break terminates the loop entirely, while skip (often implemented as continue) skips the current iteration. In the example, the loop prints numbers 1-10 but skips 5 using continue and stops entirely at 8 using break, showcasing how to conditionally bypass steps or exit early based on specific logic.

#include <iostream>
using namespace std;

int main() {
    cout << "Numbers 1-10, skipping 5, stopping at 8:" << endl;
    
    for (int i = 1; i <= 10; i++) {
        if (i == 5) {
            cout << "Skipping " << i << endl;
            continue;  // Skip rest of this iteration
        }
        
        if (i == 8) {
            cout << "Breaking at " << i << endl;
            break;     // Exit the loop completely
        }
        
        cout << "Number: " << i << endl;
    }
    
    cout << "Loop finished!" << endl;
    
    return 0;
}