How to Loop Over an Array in C++

1. Use the for Loop to Iterate Over an Array
2. Use Range-based Loop to Iterate Over an Array
3. Use std::for_each Algorithm to Iterate Over an Array

This article will explain how to iterate over an array using different methods in C++.

Use the for Loop to Iterate Over an Array

The apparent method to iterate over array elements is a for loop. It consists of a three-part statement, each separated with commas. First, we should initialize the counter variable - i, which is executed only once by design. The next part declares a condition that will be evaluated on each iteration, and if the false is returned, the loop stops running. In this case, we compare the counter and the size of the array. The last part increments the counter, and it is also executed on each loop cycle.

#include <array>
#include <iostream>

using std::array;
using std::cin;
using std::cout;
using std::endl;
using std::string;

int main() {
  array<string, 10> str_arr = {"Albatross", "Auklet", "Bluebird", "Blackbird",
                               "Cowbird",   "Dove",   "Duck",     "Godwit",
                               "Gull",      "Hawk"};

  for (size_t i = 0; i < str_arr.size(); ++i) {
    cout << str_arr[i] << " - ";
  }
  cout << endl;

  return EXIT_SUCCESS;
}

Output:

Albatross - Auklet - Bluebird - Blackbird - Cowbird - Dove - Duck - Godwit - Gull - Hawk -

Use Range-based Loop to Iterate Over an Array

The range-based loop is the readable version of the traditional for loop. This method is a powerful alternative as it offers easy iteration over complicated containers and still maintains flexibility for accessing each element. The following code sample is the exact reimplementation of the previous example:

#include <array>
#include <iostream>

using std::array;
using std::cin;
using std::cout;
using std::endl;
using std::string;

int main() {
  array<string, 10> str_arr = {"Albatross", "Auklet", "Bluebird", "Blackbird",
                               "Cowbird",   "Dove",   "Duck",     "Godwit",
                               "Gull",      "Hawk"};

  for (auto &item : str_arr) {
    cout << item << " - ";
  }
  cout << endl;

  return EXIT_SUCCESS;
}

Use std::for_each Algorithm to Iterate Over an Array

for_each is a powerful STL algorithm to operate on range elements and apply custom defined functions. It takes range starting and last iterator objects as the first two parameters, and the function object as the third one. In this case, we declare a function object as lambda expression, which directly outputs the calculated results to the console. Lastly, we can pass the custom_func variable as an argument to for_each method to operate on array elements.

#include <array>
#include <iostream>

using std::array;
using std::cin;
using std::cout;
using std::endl;
using std::for_each;
using std::string;

int main() {
  array<int, 10> int_arr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  auto custom_func = [](auto &i) { cout << i * (i + i) << "; "; };
  ;

  for_each(int_arr.begin(), int_arr.end(), custom_func);
  cout << endl;

  return EXIT_SUCCESS;
}

Output:

2; 8; 18; 32; 50; 72; 98; 128; 162; 200;