Vector loop

Learn to iterate over a vector with range-based for.

Looping with range-based for

The range-based for loop is a short way to walk through every element of a vector in order. Its form is for (int x : nums) { std::cout << x; }. Here x takes one element of the vector each turn; you do not handle an index.

This form is ideal when you only read or print elements. When no index is needed, range-based for is preferred over the classic for; it is less error-prone. Modifying the element requires a reference, which we cover in a later level.

Modifying inside the loop

In a range-based for you get a copy of the element; changes to x do not affect the vector. for (int x : nums) { x = 0; } only zeros the local copy, not nums.

To change the vector itself you need a reference, which you will see in the references topic. For now use range-based for only for reading and printing; when you need to modify elements, you will need a classic for or a reference.

Exercise Print with range-based for

Declare std::vector<int> nums = {2, 4, 6, 8};. Print every element on a single line, adjacent to each other, using a range-based for.

Show example solution

#include <iostream>
#include <vector>

int main() {
    std::vector<int> nums = {2, 4, 6, 8};
    for (int x : nums) {
        std::cout << x;
    }
    std::cout << std::endl;
    return 0;
}

Test yourself

Match the loop forms

for (int x : nums)

Range-based for
for (int i = 0; ...)

Classic for
nums.size()

Loop bound
std::cout << x

Print the element
What does for (int x : nums) { std::cout << x; } print? (nums = {1, 2, 3})
```
std::vector<int> nums = {1, 2, 3};
for (int x : nums) { std::cout << x; }
```
- 1 2 3
- 3 2 1
- 6
- 123
Show answer

123 — each element is printed without separator: 123.

Complete the range-based for

for (int x ____ nums) { std::cout << x; }

Show answer

for (int x : nums) { std::cout << x; }

Next lesson: Summary - std::vector

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