C++ Loops Tutorial: for, while, and do-while Explained

Imagine you need to print the numbers 1 to 100. Without loops, you’d write 100 separate std::cout statements. With a loop, it’s three lines. Loops are one of the most fundamental building blocks in programming — they let you repeat a block of code without repeating yourself.

C++ has three loop types: for, while, and do-while. Each fits a different situation. This tutorial explains all three from scratch, with clear examples.

The for Loop

The for loop is the most common loop in C++. Use it when you know exactly how many times you want to repeat something.

for (initialisation; condition; update) {
    // body — runs each time condition is true
}

A concrete example — print numbers 1 to 5:

#include <iostream>

int main() {
    for (int i = 1; i <= 5; i++) {
        std::cout << i << std::endl;
    }
    return 0;
}

Output:

1
2
3
4
5

Breaking down what happens on each iteration:

Counting Down

You can count in any direction:

for (int i = 5; i >= 1; i--) {
    std::cout << i << " ";
}
// Output: 5 4 3 2 1

Counting by Steps

for (int i = 0; i <= 20; i += 5) {
    std::cout << i << " ";
}
// Output: 0 5 10 15 20

Nested for Loops

A loop inside a loop. The inner loop completes all its iterations for each iteration of the outer loop:

for (int row = 1; row <= 3; row++) {
    for (int col = 1; col <= 3; col++) {
        std::cout << row << "x" << col << "=" << row * col << "  ";
    }
    std::cout << std::endl;
}

Output:

1x1=1  1x2=2  1x3=3  
2x1=2  2x2=4  2x3=6  
3x1=3  3x2=6  3x3=9  

The Range-Based for Loop (C++11)

When iterating over a collection — an array, vector, or string — the range-based for loop is cleaner:

#include <iostream>
#include <vector>

int main() {
    std::vector<int> scores = {85, 92, 78, 95, 88};

    for (int score : scores) {
        std::cout << score << " ";
    }
    // Output: 85 92 78 95 88

    return 0;
}

This reads as “for each score in scores” — no index, no size, no off-by-one risk.

For large objects like strings, use const reference to avoid copying:

std::vector<std::string> names = {"Alice", "Bob", "Carol"};

for (const std::string& name : names) {
    std::cout << name << std::endl;
}

The while Loop

The while loop repeats as long as a condition is true. Use it when you don’t know in advance how many times you’ll loop.

while (condition) {
    // body
}

A simple example — keep halving a number until it’s less than 1:

#include <iostream>

int main() {
    double value = 100.0;

    while (value >= 1.0) {
        std::cout << value << std::endl;
        value /= 2;
    }

    return 0;
}

Output:

100
50
25
12.5
6.25
3.125
1.5625

Reading User Input with while

while loops are natural for input validation:

#include <iostream>

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

    while (number <= 0) {
        std::cout << "Invalid. Enter a positive number: ";
        std::cin >> number;
    }

    std::cout << "You entered: " << number << std::endl;
    return 0;
}

The loop keeps asking until the user provides valid input. You can’t know in advance how many tries they’ll need — so while is the right choice here.

Infinite Loops

A while (true) loop runs forever until you explicitly break out of it:

while (true) {
    // do something
    if (exitCondition) {
        break;  // exit the loop
    }
}

This pattern is common in game loops, server loops, and menu systems.

The do-while Loop

The do-while loop is like a while loop, but the body always runs at least once — the condition is checked after the first execution.

do {
    // body — runs at least once
} while (condition);

The most natural use case: menus where you always want to show the options at least once:

#include <iostream>

int main() {
    int choice;

    do {
        std::cout << "\n--- Menu ---\n";
        std::cout << "1. Start game\n";
        std::cout << "2. Settings\n";
        std::cout << "3. Quit\n";
        std::cout << "Enter choice: ";
        std::cin >> choice;
    } while (choice != 3);

    std::cout << "Goodbye!" << std::endl;
    return 0;
}

The menu shows first, then checks if the user chose quit. With a regular while, you’d need to show the menu before the loop too — do-while avoids that duplication.

break and continue

break — Exit the Loop Early

break immediately exits the loop, regardless of the condition:

#include <iostream>

int main() {
    for (int i = 1; i <= 10; i++) {
        if (i == 6) {
            break;  // stop when we hit 6
        }
        std::cout << i << " ";
    }
    // Output: 1 2 3 4 5
    return 0;
}

Common use: searching for a value and stopping once found.

std::vector<int> data = {4, 7, 2, 9, 1, 5};
int target = 9;
bool found = false;

for (int i = 0; i < data.size(); i++) {
    if (data[i] == target) {
        std::cout << "Found " << target << " at index " << i << std::endl;
        found = true;
        break;  // no need to keep searching
    }
}

continue — Skip to Next Iteration

continue skips the rest of the current iteration and jumps to the next:

for (int i = 1; i <= 10; i++) {
    if (i % 2 == 0) {
        continue;  // skip even numbers
    }
    std::cout << i << " ";
}
// Output: 1 3 5 7 9

Choosing the Right Loop

In practice, for and range-based for cover the vast majority of cases. while is used for user input, event processing, and anything that reads until a condition changes. do-while is relatively rare — mainly menus and input prompts.

Common Mistakes

Off-by-one error:

// Wrong — prints 0 to 9, missing 10
for (int i = 0; i < 10; i++) { ... }  // if you wanted 1-10

// Correct — prints 1 to 10
for (int i = 1; i <= 10; i++) { ... }

Forgetting to update in a while loop (infinite loop):

int i = 0;
while (i < 5) {
    std::cout << i << std::endl;
    // Missing: i++
    // This runs forever!
}

Modifying the loop variable inside the body:

for (int i = 0; i < 10; i++) {
    std::cout << i << std::endl;
    i += 2;  // skips elements unexpectedly; hard to reason about
}
// Better: use the update expression to control step size
for (int i = 0; i < 10; i += 3) { ... }

A Practical Example: Number Guessing Game

#include <iostream>
#include <cstdlib>
#include <ctime>

int main() {
    srand(time(0));
    int secret = rand() % 100 + 1;  // random number 1-100
    int guess;
    int attempts = 0;

    std::cout << "Guess the number (1-100):" << std::endl;

    do {
        std::cout << "Your guess: ";
        std::cin >> guess;
        attempts++;

        if (guess < secret) {
            std::cout << "Too low!" << std::endl;
        } else if (guess > secret) {
            std::cout << "Too high!" << std::endl;
        }
    } while (guess != secret);

    std::cout << "Correct! You got it in " << attempts << " attempts." << std::endl;

    return 0;
}

This uses do-while because we always want at least one guess, and we don’t know how many guesses the player will need.

Summary

C++ has three loop types: for (known iteration count), while (unknown count, condition first), and do-while (unknown count, body first). The range-based for loop from C++11 simplifies iterating over collections. Use break to exit early and continue to skip an iteration.

The most important habit: always double-check your loop condition and update expression before running. Off-by-one errors and accidental infinite loops are the two most common loop bugs.

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Related Articles

• C++ Variables and Data Types: A Complete Beginner’s Guide — variables are what loops operate on; make sure you understand them first.
• C++ Arrays Tutorial: Store and Access Multiple Values — loops and arrays are used together constantly; learn how to iterate arrays properly.
• C++ Functions Tutorial: How to Write and Use Functions — once you understand loops, wrapping them in functions is the next step.