C++ Looping Through Arrays

A for loop with an index, or a range-based for loop, is the standard way to visit every element of an array in C++, whether printing, summing, searching, or modifying values.

In this page:

Looping Through an Array with a for Loop
Looping with Range-Based for
Summing Array Elements
Finding a Value in an Array
Modifying Elements in a Loop

Looping Through an Array with a for Loop

The standard way to loop through an array in C++ is a for loop whose index variable runs from 0 up to, but not including, the array's length, accessing one element per iteration with square-bracket indexing.

Example: Looping Through an Array with a for Loop

cpp

#include <iostream>

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

Looping with Range-Based for

A range-based for loop iterates directly over an array's elements without needing an explicit index variable, making the loop shorter and less error-prone.

Example: Looping with Range-Based for

cpp

#include <iostream>

int main() {
	int arr[] = {1, 2, 3, 4};
	for (int value : arr) {
		std::cout << value << " ";
	}
	std::cout << std::endl;
	return 0;
}

Summing Array Elements

A running total variable, initialized before the loop and updated inside it, is the standard pattern for summing every element in an array, which can then be divided by the count to compute an average.

Example: Summing Array Elements

cpp

#include <iostream>

int main() {
	int arr[] = {10, 20, 30};
	int total = 0;
	for (int i = 0; i < 3; i++) {
		total += arr[i];
	}
	std::cout << total << std::endl;
	return 0;
}

Finding a Value in an Array

Searching an array for a specific value loops through its elements checking each one against the target, and break is commonly used to stop the loop immediately once a match is found rather than continuing needlessly.

Example: Finding a Value in an Array

cpp

#include <iostream>

int main() {
	int arr[] = {5, 8, 12, 3};
	int target = 12;
	for (int i = 0; i < 4; i++) {
		if (arr[i] == target) {
			std::cout << "Found at index " << i << std::endl;
			break;
		}
	}
	return 0;
}

Modifying Elements in a Loop

A loop can modify an array's elements in place by both reading and writing to the same index within its body, which is how operations like doubling every value or clamping negative values are applied across an entire array.

Example: Modifying Elements in a Loop

cpp

#include <iostream>

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

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