Arrays in C++

An array stores multiple values of the same data type in a single variable.

int marks[5];

Here, marks is an array that can store five integer values.

Arrays are useful when we need to store many related values.

• Store multiple values using one variable name.
• Reduce repeated variable declarations.
• Make it easier to process collections of data.
• Allow values to be accessed using indexes.
• Work naturally with loops.

For example, five marks can be stored in one array instead of five separate variables.

The basic syntax for declaring an array is:

dataType arrayName[size];

Example:

int numbers[5];

Here:

• int is the data type.
• numbers is the array name.
• 5 is the number of elements.

We can initialize an array when we declare it.

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

The five values are stored in the five array elements.

An array uses an index to identify each element. C++ array indexes start from 0.

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

Use the index inside square brackets to access an element.

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

std::cout << numbers[0];

Output:

10

The expression numbers[0] accesses the first element.

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

std::cout << numbers[4];

Output:

50

For an array containing five elements, the last index is 4.

An array element can be changed by assigning a new value to its index.

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

numbers[2] = 100;

std::cout << numbers[2];

Output:

100

A loop can be used to print every element of an array.

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

for (int i = 0; i < 5; i++) {

    std::cout << numbers[i] << std::endl;
}

Output:

10
20
30
40
50

We can use a loop to take values from the user.

int numbers[5];

for (int i = 0; i < 5; i++) {

    std::cin >> numbers[i];
}

Each input value is stored at a different index.

#include <iostream>

int main() {

    int numbers[5];

    std::cout << "Enter 5 numbers: ";

    for (int i = 0; i < 5; i++) {
        std::cin >> numbers[i];
    }

    std::cout << "Numbers are:" << std::endl;

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

    return 0;
}

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

int sum = 0;

for (int i = 0; i < 5; i++) {

    sum += numbers[i];
}

std::cout << "Sum = " << sum;

Output:

Sum = 150

int marks[5] = {70, 80, 90, 60, 75};

int sum = 0;

for (int i = 0; i < 5; i++) {

    sum += marks[i];
}

double average = sum / 5.0;

std::cout << "Average = "
          << average;

Using 5.0 helps produce a decimal result.

int numbers[5] = {25, 80, 45, 90, 30};

int largest = numbers[0];

for (int i = 1; i < 5; i++) {

    if (numbers[i] > largest) {
        largest = numbers[i];
    }
}

std::cout << "Largest = "
          << largest;

Output:

Largest = 90

int numbers[5] = {25, 80, 45, 90, 30};

int smallest = numbers[0];

for (int i = 1; i < 5; i++) {

    if (numbers[i] < smallest) {
        smallest = numbers[i];
    }
}

std::cout << "Smallest = "
          << smallest;

Output:

Smallest = 25

int numbers[6] = {10, 15, 20, 25, 30, 35};

int count = 0;

for (int i = 0; i < 6; i++) {

    if (numbers[i] % 2 == 0) {
        count++;
    }
}

std::cout << "Even numbers = "
          << count;

The modulus operator checks whether an element is divisible by 2.

int numbers[6] = {10, 15, 20, 25, 30, 35};

int count = 0;

for (int i = 0; i < 6; i++) {

    if (numbers[i] % 2 != 0) {
        count++;
    }
}

std::cout << "Odd numbers = "
          << count;

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

for (int i = 4; i >= 0; i--) {

    std::cout << numbers[i] << " ";
}

Output:

50 40 30 20 10

The loop starts from the last index and moves toward index 0.

An array can also store characters.

char letters[5] = {'A', 'B', 'C', 'D', 'E'};

for (int i = 0; i < 5; i++) {

    std::cout << letters[i] << " ";
}

Output:

A B C D E

A character array can be initialized using a string literal.

char name[] = "Rahul";

std::cout << name;

C++ stores the characters along with a terminating null character '\0'.

For modern C++ programs, std::string is generally more convenient for working with text.

The sizeof operator can be used to determine the total number of bytes occupied by an array.

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

std::cout << sizeof(numbers);

To calculate the number of elements in an array in the same scope, we can use:

int size = sizeof(numbers) / sizeof(numbers[0]);

If an array is initialized with fewer values than its declared size, the remaining elements are value-initialized.

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

for (int i = 0; i < 5; i++) {

    std::cout << numbers[i] << " ";
}

Output:

10 20 0 0 0

When an array is initialized with values, its size can be omitted. The compiler determines the size from the initializer.

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

This array contains five elements.

void display(int numbers[], int size) {

    for (int i = 0; i < size; i++) {

        std::cout << numbers[i] << " ";
    }
}

int main() {

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

    display(numbers, 5);

    return 0;
}

An array can be passed to a function along with its size.

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

int search = 30;
bool found = false;

for (int i = 0; i < 5; i++) {

    if (numbers[i] == search) {

        found = true;
        break;
    }
}

if (found) {
    std::cout << "Value found";
}
else {
    std::cout << "Value not found";
}

• Using an index outside the valid range.
• Forgetting that array indexes start from 0.
• Using the wrong array size in a loop.
• Reading an element before assigning a meaningful value.
• Confusing the number of elements with the last index.
• Accidentally modifying an element at the wrong index.

#include <iostream>

int main() {

    int marks[5];

    int sum = 0;

    std::cout << "Enter marks of 5 subjects:"
              << std::endl;

    for (int i = 0; i < 5; i++) {

        std::cin >> marks[i];

        sum += marks[i];
    }

    double average = sum / 5.0;

    std::cout << "Total = "
              << sum << std::endl;

    std::cout << "Average = "
              << average;

    return 0;
}

#include <iostream>

int main() {

    int numbers[5];

    std::cout << "Enter 5 numbers:"
              << std::endl;

    for (int i = 0; i < 5; i++) {

        std::cin >> numbers[i];
    }

    int largest = numbers[0];

    for (int i = 1; i < 5; i++) {

        if (numbers[i] > largest) {

            largest = numbers[i];
        }
    }

    std::cout << "Largest = "
              << largest;

    return 0;
}

• Use meaningful array names.
• Keep track of the number of elements.
• Use loops instead of repeating the same code.
• Remember that indexes start at 0.
• Never intentionally access an index outside the valid range.
• Initialize arrays when appropriate.
• Pass the array size when a function needs it.
• Use std::array or std::vector when their features are more suitable than a built-in array.

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

for (int i = 0; i < 5; i++) {

    std::cout << numbers[i] << " ";
}