Arrays to Functions

Passing arrays to functions in C

In C programming, an array can be passed to a function so that the function can process its elements. For example, a function can calculate the sum, average, or largest element of an array.

Definition

Passing an array to a function means providing the array's starting address to a function so that it can access and process the array elements.

In C, when an array is passed as a function argument, it is adjusted to a pointer to its first element. The array elements are not copied into a new array.

Syntax

return_type function_name(data_type array[], int size);

Example:

void display(int a[], int size);

Here:
- void means the function does not return a value.
- int a[] represents the array parameter.
- size specifies the number of elements the function should process.

Example 1: C Program passing an array to display its elements

#include 

void display(int a[], int size)
{
    int i;

    for (i = 0; i < size; i++)
    {
        printf("%d ", a[i]);
    }
}

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

    display(numbers, 5);

    return 0;
}

Output:

10 20 30 40 50

How does it work?

1. Calling function: display(numbers, 5); The array name provides access to its first element, and 5 provides the number of elements.
2. Receiving parameters: void display(int a[], int size) The parameter a can access the original array elements, and size is 5.
3. Processing elements: The loop accesses a[0], a[1], a[2], a[3], and a[4] and displays each value.

Example 2: C Program passing an array to calculate the sum

#include 

int calculateSum(int a[], int size)
{
    int i, sum = 0;

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

    return sum;
}

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

    result = calculateSum(a, 5);

    printf("Sum = %d\n", result);

    return 0;
}

Output:

Sum = 150

The function receives the array and its size, adds all the elements, and returns the sum to main().

Modifying array elements inside a function

A function can also modify the original array elements because its array parameter provides access to those elements.

#include 

void doubleElements(int a[], int size)
{
    int i;

    for (i = 0; i < size; i++)
    {
        a[i] = a[i] * 2;
    }
}

int main(void)
{
    int a[4] = {1, 2, 3, 4};
    int i;

    doubleElements(a, 4);

    for (i = 0; i < 4; i++)
    {
        printf("%d ", a[i]);
    }

    return 0;
}

Output:

2 4 6 8

The original array is modified. This happens because the function accesses the same array elements through its parameter.

Passing a two-dimensional array to a function

For a two-dimensional array, the number of columns must be specified in the function parameter type.

#include 

void display(int a[][3], int rows)
{
    int i, j;

    for (i = 0; i < rows; i++)
    {
        for (j = 0; j < 3; j++)
        {
            printf("%d ", a[i][j]);
        }
        printf("\n");
    }
}

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

    display(a, 2);

    return 0;
}

Output:

1 2 3
4 5 6

Notice that int a[][3] leaves the row count unspecified but specifies the column count as 3.

Practice questions

1. Explain how arrays are passed to functions in C with a suitable example.
2. Write a C program to calculate the sum of array elements using a function.
3. Explain how a function can modify array elements.
4. Explain how a two-dimensional array is passed to a function.