C++ Arrays – Definition, Syntax, Initialization, and Examples

Introduction to Arrays in C++

In C++ programming, an array is a collection of elements of the same data type, stored in contiguous memory locations. Each element can be accessed using an index.

👉 Example:
Instead of creating 100 different variables to store the ages of 100 people, you can create a single integer array of size 100:

int Age[100];

int Age[100];

Here, all 100 values are stored in continuous memory, where:

• The lowest memory address corresponds to Age[0].
• The highest memory address corresponds to Age[99].

✅ This makes arrays efficient and easier to use.

Array Diagram –

Declaring Arrays in C++

The basic syntax is:

type arrayName[arraySize];

type arrayName[arraySize];

• type → Data type of elements (int, float, char, etc.)
• arrayName → Name of the array
• arraySize → Must be an integer constant greater than 0

✅ Example:

double Arr[5];   // Array of 5 doubles
int marks[10];   // Array of 10 integers
char letters[26]; // Array of 26 characters

double Arr[5];   // Array of 5 doubles
int marks[10];   // Array of 10 integers
char letters[26]; // Array of 26 characters

Initializing Arrays

You can initialize arrays in multiple ways:

1. Direct Initialization

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

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

2. Partial Initialization

If fewer elements are given, remaining ones are initialized to 0:

int numbers[5] = {10, 20}; // {10, 20, 0, 0, 0}

int numbers[5] = {10, 20}; // {10, 20, 0, 0, 0}

3. Implicit Size

If the size is omitted, it is automatically determined:

int numbers[] = {1, 2, 3, 4, 5}; // size = 5

int numbers[] = {1, 2, 3, 4, 5}; // size = 5

4. Single Element Assignment

int marks[5];
marks[0] = 95;   // Assigning value to first element
marks[4] = 88;   // Assigning value to fifth element

int marks[5];
marks[0] = 95;   // Assigning value to first element
marks[4] = 88;   // Assigning value to fifth element

⚠️ Note: Array indices start from 0. So for an array of size n, valid indices range from 0 to n-1.

Accessing Array Elements

You can access elements using their index:

cout << marks[0]; // prints first element
cout << marks[4]; // prints fifth element

cout << marks[0]; // prints first element
cout << marks[4]; // prints fifth element

To traverse all elements, loops are commonly used:

for(int i=0; i<5; i++) {
    cout << marks[i] << endl;
}

for(int i=0; i<5; i++) {
    cout << marks[i] << endl;
}

Example Program: Arrays in C++

#include<iostream>
using namespace std;

int main() {
    // Declaration & initialization
    int arr[3] = {1, 2, 3};  
    double arr1[5];         
    arr1[0] = 1.456;        
    arr1[1] = 36.765;
    
    char myarr[4];          
    myarr[0] = 'a';         

    // Taking input in array
    int temp_arr[5];
    cout << "Enter 5 integers:" << endl;
    for(int i=0; i<5; i++) {
        cin >> temp_arr[i];
    }

    // Displaying array values
    cout << "The values you entered are:" << endl;
    for(int i=0; i<5; i++) {
        cout << temp_arr[i] << endl;
    }

    return 0;
}

#include<iostream>
using namespace std;

int main() {
    // Declaration & initialization
    int arr[3] = {1, 2, 3};  
    double arr1[5];         
    arr1[0] = 1.456;        
    arr1[1] = 36.765;
    
    char myarr[4];          
    myarr[0] = 'a';         

    // Taking input in array
    int temp_arr[5];
    cout << "Enter 5 integers:" << endl;
    for(int i=0; i<5; i++) {
        cin >> temp_arr[i];
    }

    // Displaying array values
    cout << "The values you entered are:" << endl;
    for(int i=0; i<5; i++) {
        cout << temp_arr[i] << endl;
    }

    return 0;
}

📌 Sample Output:

Enter 5 integers:
10 20 30 40 50
The values you entered are:
10
20
30
40
50

Enter 5 integers:
10 20 30 40 50
The values you entered are:
10
20
30
40
50

Key Points About Arrays

• Arrays always start with index 0.
• Size of the array must be fixed at declaration.
• Accessing out-of-bounds elements leads to undefined behavior.
• Arrays can be traversed easily with loops.
• Arrays are stored in contiguous memory blocks.

Conclusion

Arrays are a fundamental concept in C++ that make handling multiple values of the same type efficient and simple.
They form the foundation for advanced data structures like strings, matrices, and pointers.

👉 Next, you should explore Multi-Dimensional Arrays to learn how arrays can represent tables and matrices.