C++ Range Based For Loop
The range-based for loop is a modern, clean way to visit every element in a collection such as an array or a vector. Instead of managing an index and worrying about going out of bounds, you just say, for each item in this collection, do something. It was introduced in C++11 and is now the go-to way to loop over data.
Looping over a collection
The syntax reads almost like English: for a declared variable, colon, then the collection. On each pass, the variable holds the next element from the collection until every element has been visited.
Looping through an array
#include <iostream>
using namespace std;
int main() {
int numbers[] = {10, 20, 30, 40};
for (int n : numbers) {
cout << n << "\n";
}
return 0;
}There is no index to manage and no length to calculate. The loop automatically handles every element from the first to the last, which removes a whole category of off-by-one mistakes.
Reading versus changing elements
If you only need to read the values, a plain copy like int n is fine. If you want to modify the elements in place, add an ampersand to make the variable a reference to the real element.
Doubling every value with a reference
#include <iostream>
using namespace std;
int main() {
int prices[] = {5, 8, 12};
for (int &p : prices) {
p = p * 2;
}
for (int p : prices) {
cout << p << "\n";
}
return 0;
}- for (int n : arr) makes a copy of each element, so changes do not affect the original.
- for (int &n : arr) refers to the actual element, so changes stick.
- for (auto n : arr) lets the compiler deduce the element type.
Choose the range-based for loop when you want to touch every element and you do not need the index. If you need the position number, a classic for loop with an index is still the right tool.
