How to Use Range Based For Loop in C++: Syntax and Examples

In C++, use the range-based for loop to iterate over elements of a container or array easily with the syntax for (auto element : container). This loop automatically goes through each item without needing an index or iterator.

Syntax

The range based for loop has this basic form:

for (declaration : container) {
    // code using declaration
}

declaration is a variable that represents each element in the container one by one.
container is any array, vector, or container you want to loop through.

This loop runs once for each element in the container.

cpp

for (auto element : container) {
    // use element
}

Example

This example shows how to use a range based for loop to print all numbers in an array.

cpp

#include <iostream>

int main() {
    int numbers[] = {10, 20, 30, 40, 50};
    for (auto num : numbers) {
        std::cout << num << " ";
    }
    std::cout << std::endl;
    return 0;
}

Output

10 20 30 40 50 

Common Pitfalls

One common mistake is modifying elements inside the loop without using references, which only changes a copy, not the original element.

Wrong way (does not change original):

for (auto x : container) {
    x = x + 1; // changes copy only
}

Right way (use reference to modify original):

for (auto &x : container) {
    x = x + 1; // changes original element
}

Also, avoid using auto if you want to be explicit about the element type.

Quick Reference

Tips for using range based for loops:

• Use auto to let the compiler infer the element type.
• Use & to get a reference if you want to modify elements.
• Use const auto & if you only want to read elements without copying.
• Works with arrays, vectors, lists, and other containers supporting begin() and end().

Key Takeaways

Use range based for loops to iterate easily over containers without manual indexing.

Use references in the loop variable to modify original elements.

Use const references to avoid copying when only reading elements.

Range based for loops work with arrays and standard containers like vector and list.

Avoid modifying loop variables without references as it only changes copies.