Arrays

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MamtaWardhani
Published May 6, 2021Updated Jun 20, 2025
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An array is a data structure that stores multiple values of the same data type in contiguous memory locations. Arrays allow storing and accessing a collection of elements efficiently using a single variable name with indexed positions. Instead of declaring separate variables for each value, an array provides a way to manage multiple related values as a single entity.

Arrays are particularly useful when dealing with collections of similar data, such as storing student grades, temperature readings, or inventory items. The size of an array must be known at compile time and cannot be changed during program execution.

Create an Array

Syntax

dataType arrayName[arraySize];

The syntax consists of the data type, followed by the array name, and the size enclosed in square brackets. The size must be a positive integer constant.

Example

This example creates three arrays: numbers can store 5 integers, prices can store 10 double values, and letters can store 26 characters.

#include <iostream>
using namespace std;


int main() {
  // Create an array of integers
  int numbers[5];


  // Create an array of doubles
  double prices[10];


  // Create an array of characters
  char letters[26];


  return 0;
}

Initialize Array with Values

Syntax

dataType arrayName[arraySize] = {value1, value2, value3, ...};

Values are enclosed in curly braces and separated by commas. The number of values cannot exceed the array size but can be less.

Example

In the following example, scores is fully initialized, grades has the first three elements set with the rest defaulting to 0, and ages automatically sizes to 5 elements.

#include <iostream>
using namespace std;


int main() {
  // Initialize array with specific values
  int scores[5] = {85, 92, 78, 96, 88};


  // Initialize with fewer values (remaining filled with 0)
  int grades[6] = {90, 85, 77};


  // Let compiler determine size
  int ages[] = {25, 30, 35, 28, 33};


  return 0;
}

Access Array Elements

Array elements are accessed using the subscript operator [] with an index number. Array indexing starts at 0, meaning the first element is at index 0, the second at index 1, and so on.

Example

The following code initializes an array of five integers and prints the first, third, and last elements:

#include <iostream>
using namespace std;


int main() {
  int numbers[5] = {10, 20, 30, 40, 50};


  // Access and print array elements
  cout << "First element: " << numbers[0] << endl;
  cout << "Third element: " << numbers[2] << endl;
  cout << "Last element: " << numbers[4] << endl;


  return 0;
}

The output of the above code will be:

First element: 10
Third element: 30
Last element: 50

Update Array Elements

Array elements can be modified by assigning new values to specific indices using the assignment operator.

Example

The following code initializes an array of five integers, prints the original array, updates specific elements, and then prints the updated array:

#include <iostream>
using namespace std;


int main() {
  int numbers[5] = {10, 20, 30, 40, 50};


  cout << "Original array: ";
  for (int i = 0; i < 5; i++) {
    cout << numbers[i] << " ";
  }
  cout << endl;


  // Update specific elements
  numbers[0] = 15;
  numbers[2] = 35;
  numbers[4] = 55;


  cout << "Updated array: ";
  for (int i = 0; i < 5; i++) {
    cout << numbers[i] << " ";
  }
  cout << endl;


  return 0;
}

The output of the above code will be:

Original array: 10 20 30 40 50
Updated array: 15 20 35 40 55

Example 1: Student Grade Calculator

The following code initializes an array of student grades, calculates their total and average, and prints the results:

#include <iostream>
using namespace std;


int main() {
  // Create and initialize array of student grades
  double grades[6] = {88.5, 92.0, 76.5, 85.0, 91.5, 89.0};
  double sum = 0.0;


  cout << "Student Grades: ";


  // Display grades and calculate sum
  for (int i = 0; i < 6; i++) {
    cout << grades[i] << " ";
    sum += grades[i];
  }


  double average = sum / 6;


  cout << endl;
  cout << "Total: " << sum << endl;
  cout << "Average: " << average << endl;


  return 0;
}

The output of the above example will be:

Student Grades: 88.5 92 76.5 85 91.5 89
Total: 522.5
Average: 87.0833

Example 2: Interactive Array Management

The following code takes 5 integers from the user, doubles every second element in the array, displays the original and updated arrays, and finds and prints the maximum value along with its index:

#include <iostream>
using namespace std;


int main() {
  const int SIZE = 5;
  int numbers[SIZE];


  // Input values from user
  cout << "Enter " << SIZE << " integers:" << endl;
  for (int i = 0; i < SIZE; i++) {
    cout << "Element " << (i + 1) << ": ";
    cin >> numbers[i];
  }


  // Display original array
  cout << "\nOriginal array: ";
  for (int i = 0; i < SIZE; i++) {
    cout << numbers[i] << " ";
  }
  cout << endl;


  // Update every second element
  cout << "\nUpdating every second element..." << endl;
  for (int i = 1; i < SIZE; i += 2) {
    numbers[i] = numbers[i] * 2;
  }


  // Display updated array
  cout << "Updated array: ";
  for (int i = 0; i < SIZE; i++) {
    cout << numbers[i] << " ";
  }
  cout << endl;


  // Find maximum value
  int max = numbers[0];
  int maxIndex = 0;
  for (int i = 1; i < SIZE; i++) {
    if (numbers[i] > max) {
      max = numbers[i];
      maxIndex = i;
    }
  }


  cout << "\nMaximum value: " << max << " at index " << maxIndex << endl;


  return 0;
}

The output of the above code will be:

Enter 5 integers:
Element 1: 1
Element 2: 2
Element 3: 5
Element 4: 5
Element 5: 2


Original array: 1 2 5 5 2


Updating every second element...
Updated array: 1 4 5 10 2


Maximum value: 10 at index 3

Note: The output of this program will vary depending on the user’s input values.

Frequently Asked Questions

1. Can array size be changed after declaration?

No, the size of an array is fixed at compile time and cannot be modified during program execution. If dynamic sizing is needed, consider using std::vector instead.

2. What happens if I access an array element beyond its bounds?

Accessing elements outside the valid index range (0 to size-1) leads to undefined behavior, which can cause program crashes or unpredictable results. Always ensure indices are within valid bounds.

3. How to find the length of an array?

Use the sizeof operator: int length = sizeof(array) / sizeof(array[0]);. This only works for statically declared arrays, not for arrays passed as function parameters.

4. Can arrays store different data types?

No, all elements in an array must be of the same data type. To store different types, consider using structures, classes, or std::variant (C++17).

5. How are array elements stored in memory?

Array elements are stored in contiguous memory locations, with each element directly adjacent to the next. This provides efficient memory access and enables pointer arithmetic.

Arrays

.at()
Returns a reference to the element at the specified position with bounds checking in std::array containers.
.cbegin
Returns a constant iterator to the beginning of a container.
.crbegin()
Returns a const_reverse_iterator pointing to the last element of the given array.

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