Array Basics

An array is a fundamental data structure in C++ that provides a contiguous block of memory for storing multiple values of the same type. Because arrays can hold elements of any data type—integers, floating-point numbers, characters, or even complex objects—they are a versatile way to manage collections of data.

Declaring Arrays

To declare an array use the following structure:

type variable_name [kSizeConstant];

The following is an integer array that can hold up to 5 values:

const int kSize = 4;
int array [kSize];

Note

We are using static arrays meaning the size must be set when the array is declared, and can NOT change during the course of the program.

Tip

Use constant variables for the array’s size so that modifications to the size can be made in one place.

Declaring an array does not automatically initialize its values. If no initial values are provided, the contents of the array elements are indeterminate.

You can initialize an array at the time of declaration by assigning it a list of values enclosed in braces {}. These values must be separated by commas, and the compiler will determine the size of the array based on the number of values provided.

int array[] = {1, 2, 3, 4, 5};

Note

You can only initialize the array with a list in the array declaration.

Tip

You can leave out the size of the array when using a list to initialize the array in the declaration. The array’s size will be the number of values in the initialization list.

When creating an array of numeric values, if you include the size of the array and use an initialization list, any values left out of the list will be set to 0. For example,

int my_array[5] = { 14 }; // 14, 0, 0, 0, 0

Using Arrays

In C++, the name of an array refers to the memory address of its first element. This means that when you write the array’s name by itself, you’re essentially 🫵 pointing to the starting position of the array in memory.

// A location in your computer like: 0x7ffc6b2fc1d0
cout << array_name << endl;

To access individual elements, you use the array’s name followed by square brackets containing the element’s index [integer]. The following is an example of how to access elements in an array called my_array:

my_array[0]
my_array[1]
my_array[2]

Note

One key characteristic of arrays in C++ is that they are 0-based, meaning the first element is accessed at index 0, the second at index 1, and so forth.

Filling Numeric Arrays

You can use a for loop to fill a non-character array with values:

const int kSize = 4;
int array[kSize];

for (int i = 0; i < kSize; ++i) {
  cout << "Enter the number for index " << i << endl;
  cin >> array[i];
}

Printing Numeric Arrays

You can also use a for loop to print a non-character array with values:

for (int i = 0; i < kSize; ++i) {
  cout << array[i] << endl;
}

Overstepping Array Bounds

One of the most common and dangerous errors when working with arrays is accessing elements outside their valid range.

In C++, your compiler will not produce an error if you use an index outside of 0 to size - 1. Instead, it will treat the invalid index as a memory offset from the first element, potentially overwriting data that belongs to other variables or even other running programs.

This can lead to unpredictable behavior, crashes, or corrupted data.