Mastering Array Passing in C: Complete Guide with Clear Examples

In the world of C programming, arrays are fundamental tools used to store collections of data. But working with arrays becomes especially powerful when you learn how to pass them to functions. Whether you’re building an application that analyzes student scores or processes sensor data, understanding array passing in C is crucial. This guide will take you from basic syntax to in-depth examples and cover all the possible ways to pass arrays (and their elements) to functions with complete clarity.

🔢 What Does “Passing an Array to a Function” Mean?

When we pass an array to a function in C, we give that function access to the array’s elements—either to read, modify, or process them. In C, arrays are not passed by value (unlike integers or characters); instead, the memory address (pointer) of the first element is passed. So, if a function modifies an array element, the change reflects outside the function too.

✍️ Basic Syntax: How to Pass Arrays in C

Let’s start by understanding the simplest form of array passing:

#include <stdio.h>

void printArray(int arr[], int size) {
    for(int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    int data[] = {10, 20, 30, 40, 50};
    int size = sizeof(data) / sizeof(data[0]);

    printArray(data, size);

    return 0;
}

🔍 Explanation:

In this code:

• The printArray function takes an int array and its size as parameters.
• Inside main, we define the array data[] and calculate its size.
• The array is passed by reference, allowing printArray to access its elements.

🧾 Alternative Syntax Using Pointers

Since arrays are passed by reference, you can use pointers instead of array notation:

#include <stdio.h>

void printArrayUsingPointer(int *arr, int size) {
    for(int i = 0; i < size; i++) {
        printf("%d ", *(arr + i));
    }
    printf("\n");
}

int main() {
    int nums[] = {5, 10, 15, 20, 25};
    int n = sizeof(nums)/sizeof(nums[0]);

    printArrayUsingPointer(nums, n);

    return 0;
}

🧠 What’s Happening Here?

This time, printArrayUsingPointer accepts a pointer (int *arr) instead of using array notation. Yet, it behaves exactly the same. In C, arr[] and *arr are interchangeable in function parameters because both refer to the same memory.

#include <stdio.h>

void incrementArray(int arr[], int size) {
    for(int i = 0; i < size; i++) {
        arr[i] += 1;
    }
}

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

    incrementArray(numbers, 5);

    for(int i = 0; i < 5; i++) {
        printf("%d ", numbers[i]);
    }

    return 0;
}

#include <stdio.h>

void square(int x) {
    printf("Square: %d\n", x * x);
}

int main() {
    int arr[] = {3, 6, 9};

    square(arr[1]); // Passing only the second element (6)

    return 0;
}

#include <stdio.h>

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

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

    displayMatrix(matrix, 2);

    return 0;
}