Arrays in C++

An array is a collection of elements of the same data type stored in contiguous memory locations. Instead of declaring 10 separate variables, an array can hold all 10 values under a single name. Think of an array like a row of lockers — each locker is numbered and stores one item.

Declaring an Array

data_type array_name[size];

int marks[5];              // array of 5 integers
float prices[3];           // array of 3 floats
char letters[4];           // array of 4 characters

Initializing an Array

int marks[5] = {85, 90, 78, 92, 88};

If fewer values are provided, the remaining elements are set to 0:

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

Size can be omitted if values are provided at declaration:

int scores[] = {55, 70, 80, 95};   // size is automatically 4

Accessing Array Elements

Array elements are accessed using an index starting from 0.

int marks[5] = {85, 90, 78, 92, 88};

cout << marks[0] << endl;  // 85 (first element)
cout << marks[4] << endl;  // 88 (last element)

Iterating Through an Array

#include <iostream>
using namespace std;

int main() {
    int marks[5] = {85, 90, 78, 92, 88};

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

Output:

marks[0] = 85
marks[1] = 90
marks[2] = 78
marks[3] = 92
marks[4] = 88

Finding the Sum and Average

int nums[] = {10, 20, 30, 40, 50};
int sum = 0;
int size = 5;

for (int i = 0; i < size; i++) {
    sum += nums[i];
}

cout << "Sum: "     << sum             << endl;
cout << "Average: " << sum / size      << endl;

Output:

Sum: 150
Average: 30

Finding Maximum and Minimum

int nums[] = {34, 7, 89, 23, 55};
int maxVal = nums[0];
int minVal = nums[0];

for (int i = 1; i < 5; i++) {
    if (nums[i] > maxVal) maxVal = nums[i];
    if (nums[i] < minVal) minVal = nums[i];
}

cout << "Max: " << maxVal << endl;
cout << "Min: " << minVal << endl;

Output:

Max: 89
Min: 7

Two-Dimensional Arrays (2D Arrays)

A 2D array is like a table with rows and columns. It is commonly used for matrices and grids.

int matrix[2][3] = {
    {1, 2, 3},
    {4, 5, 6}
};

#include <iostream>
using namespace std;

int main() {
    int grid[2][3] = {{1, 2, 3}, {4, 5, 6}};

    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            cout << grid[i][j] << " ";
        }
        cout << endl;
    }
    return 0;
}

Output:

1 2 3
4 5 6

Passing Arrays to Functions

Arrays are passed to functions by reference (the function receives the address, not a copy):

void printArray(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
}

int main() {
    int data[] = {5, 10, 15, 20};
    printArray(data, 4);
    return 0;
}

Output:

5 10 15 20

Common Array Mistakes

Key Takeaways

• Arrays store multiple values of the same type under one name.
• Array index starts at 0 — the last element is at index size - 1.
• Loops are commonly used to traverse (go through) arrays.
• 2D arrays represent tables with rows and columns.
• Arrays passed to functions are passed by reference, not by value.