Passing arrays to functions

Notes

Passing Arrays to Functions

Definition: Passing an array to a function means providing the array to a function so that the function can access and process its elements.

Why Pass an Array to a Function?

Arrays are often passed to functions when the same collection of values needs to be processed by a separate function.

Passing a One-Dimensional Array

Definition: A one-dimensional array is passed to a function by providing the array name in the function call. The function parameter is declared as an array or an equivalent pointer parameter.

Basic Syntax

function_name(array_name, size);

Array Parameter

A function can declare an array parameter to receive the array. The size is commonly supplied separately because the function does not automatically know the number of elements in the array.

int sumArray(int arr[], int n)
{
    int sum = 0;

    for (int i = 0; i < n; i++)
        sum += arr[i];

    return sum;
}

Passing Array Size

Definition: When an array is passed to a function, the number of elements is usually passed separately so that the function knows how many elements it should process.

Accessing Elements Inside the Function

The function can access array elements using their indexes just as they are accessed in the calling function.

Important Point: Array Changes

Definition: In a normal function parameter, an array argument provides access to the same underlying array elements, so changes made to elements inside the function are visible to the calling function.

Simple Example

#include <stdio.h>

void changeFirst(int arr[])
{
    arr[0] = 100;          // modify the first array element
}

int main()
{
    int numbers[3] = {10, 20, 30};

    changeFirst(numbers);  // pass the array

    printf("%d
", numbers[0]);

    return 0;
}

Output

100

Passing Array with Size

A common function design is to pass both the array and the number of elements.

Practical Example — Find Sum of Array Elements Using a Function

Problem Statement

Write a C program to accept 5 integers in an array and pass the array to a function that calculates and returns the sum.

Learning Outcomes

• Pass a one-dimensional array to a function.
• Pass the size of the array as a separate parameter.
• Process array elements inside a function.
• Return the calculated result to the calling function.

Hint

Create a function sumArray() that accepts the array and its size. Use a loop inside the function to calculate the sum.

Theory

A one-dimensional array can be passed to a function by writing its name in the function call. The function can then access the array elements using indexes. The array size is usually passed separately.

Program

#include <stdio.h>

int sumArray(int arr[], int n);       // function declaration

int main()
{
    int arr[5];
    int i, sum;

    printf("Enter 5 numbers: ");

    // read array elements
    for (i = 0; i < 5; i++)
        scanf("%d", &arr[i]);

    sum = sumArray(arr, 5);            // pass array and its size

    printf("Sum = %d
", sum);

    return 0;
}

int sumArray(int arr[], int n)
{
    int sum = 0;

    // calculate the sum of all array elements
    for (int i = 0; i < n; i++)
        sum += arr[i];

    return sum;                         // return the calculated sum
}

Expected Output

Enter 5 numbers: 10 20 30 40 50
Sum = 150

Note

The array itself is passed using its name, while 5 is passed separately to specify the number of elements to process.

Passing an Array to a Function: Flow

Advantages of Passing Arrays to Functions

• Large arrays can be processed by separate functions.
• Programs become more modular and easier to understand.
• The same function can be reused for different arrays.
• Array elements can be processed using loops inside the function.

Passing Array vs Passing Single Variable

Important Points for Exam

• An array can be passed to a function using its name.
• The array size is usually passed separately.
• The function can access elements using indexes.
• Changes made to array elements inside the function can affect the original array.
• Arrays are commonly processed inside functions using loops.
• Passing arrays to functions improves modularity and code reuse.

Quick Revision

Important Exam Questions

Short Answer Questions

1. How is a one-dimensional array passed to a function?
2. Why is the array size commonly passed separately?
3. How are array elements accessed inside a function?
4. Can a function modify an array passed to it?
5. Write the syntax for passing an array to a function.

Long Answer Questions

1. Explain how one-dimensional arrays are passed to functions with a suitable example.
2. Write a C program to pass an array to a function and calculate the sum of its elements.
3. Explain how a function can modify the elements of an array passed to it.