Arrays and loops

Learn to iterate over arrays with for.

Arrays and loops

To process every element of an array you use a for loop. The most common pattern is for (int i = 0; i < N; i++) ... nums[i] .... Here N is the array size.

In this pattern i starts at 0, runs while below N, and on each iteration nums[i] takes one element. C-style arrays keep the size separately, so you write N by hand. With std::array you can fetch it dynamically via nums.size().

Range-based for with arrays

Besides the classic for, range-based for also works with C-style arrays: for (int x : nums) std::cout << x;. This form is shorter and safer when you do not need the index.

However, when you need the index (for example, to print the element number), the classic for is required. With std::array both range-based for and classic for via nums.size() work; both are safe. Picking the right tool for the right place improves readability.

Exercise Print the array (for)

The nums array is set to {1, 2, 3, 4, 5}. Use a for (int i = 0; i < 5; i++) loop to print each element with std::cout << nums[i]; on a single line. The output must be 12345.

Show example solution

#include <iostream>

int main() {
    int nums[5] = {1, 2, 3, 4, 5};
    for (int i = 0; i < 5; i++) {
        std::cout << nums[i];
    }
    std::cout << std::endl;
    return 0;
}

Test yourself

Match each loop part to its role

int i = 0

Start
i < 5

Condition
nums[i]

i-th element of the array
i++

Increment
What does for (int i = 0; i < 5; i++) std::cout << nums[i]; do?
```
int nums[5] = {1,2,3,4,5};
for (int i = 0; i < 5; i++)
  std::cout << nums[i];
```
- Prints the 5th element
- Prints elements 0 to 4
- Divides the array by 5
- Forms an infinite loop
Show answer

Prints elements 0 to 4 — i = 0,1,2,3,4 elements are printed.

Write the loop body

int nums[3] = {10, 20, 30};
for (int i = 0; i < 3; i++) {
    std::cout << ____;
}

Show answer

int nums[3] = {10, 20, 30};
for (int i = 0; i < 3; i++) {
    std::cout << nums[i];
}

Next lesson: Summary - Arrays

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