How to Pass 1D & 2D Arrays to Functions in C – A Practical Guide

How to Pass 1D & 2D Arrays to Functions in C

This tutorial explains how to pass entire arrays—both one‑dimensional and multi‑dimensional—to functions in C, with clear code examples and best‑practice tips.

In C, an array name decays to a pointer when passed to a function, allowing the function to operate on the original data without copying it. Understanding this behavior is essential for efficient, maintainable code.

Passing Individual Array Elements

Passing a single element is identical to passing any primitive type.

Example 1: Pass Individual Array Elements

#include <stdio.h>

void display(int age1, int age2) {
    printf("%d\n", age1);
    printf("%d\n", age2);
}

int main() {
    int ageArray[] = {2, 8, 4, 12};

    // Pass second and third elements to display()
    display(ageArray[1], ageArray[2]);
    return 0;
}

Output

8
4

Here we pass ageArray[1] and ageArray[2] just like ordinary variables. The function receives them by value, so the original array remains unchanged.

Passing Entire One‑Dimensional Arrays

To hand an entire array to a function, simply supply the array name. The function prototype must indicate an array parameter, but the actual size can be omitted. The compiler treats the parameter as a pointer to the first element.

Example 2: Compute Sum of an Array

#include <stdio.h>

float calculateSum(float num[]);

int main() {
    float result, num[] = {23.4, 55, 22.6, 3, 40.5, 18};

    // Pass the entire array to calculateSum()
    result = calculateSum(num);
    printf("Result = %.2f", result);
    return 0;
}

float calculateSum(float num[]) {
    float sum = 0.0;

    for (int i = 0; i < 6; ++i) {
        sum += num[i];
    }
    return sum;
}

Output

Result = 162.50

The function signature float calculateSum(float num[]) tells the compiler that num is a pointer to a float array. The loop processes the array in place without copying.

Passing Multi‑Dimensional Arrays

Multi‑dimensional arrays follow the same principle: the array name decays to a pointer to the first row. However, the compiler must know the size of every dimension except the first. This is required so it can calculate the correct memory offsets.

Example 3: Pass a Two‑Dimensional Array

#include <stdio.h>

void displayNumbers(int num[2][2]);

int main() {
    int num[2][2];
    printf("Enter 4 numbers:\n");
    for (int i = 0; i < 2; ++i) {
        for (int j = 0; j < 2; ++j) {
            scanf("%d", &num[i][j]);
        }
    }

    // Pass the two‑dimensional array to a function
    displayNumbers(num);
    return 0;
}

void displayNumbers(int num[2][2]) {
    printf("Displaying:\n");
    for (int i = 0; i < 2; ++i) {
        for (int j = 0; j < 2; ++j) {
            printf("%d\n", num[i][j]);
        }
    }
}

Output

Enter 4 numbers:
2
3
4
5
Displaying:
2
3
4
5

The function prototype void displayNumbers(int num[2][2]) declares a 2×2 integer array. When calling the function, we simply pass num; the compiler automatically handles the pointer conversion.

Note that you may omit the row dimension but must specify the column size: int num[][2] is valid, while the column size is essential for address calculation.

Important: C allows passing arrays to functions, but it does not support returning arrays from functions directly. Use pointers or structures if you need to return complex data.