How to Pass 2D Array to Function in C: Syntax and Example

In C, you can pass a 2D array to a function by specifying the array parameter with fixed column size, like void func(int arr[][COLS]). You must provide the number of columns so the compiler knows the memory layout. Alternatively, you can use pointers with manual indexing.

Syntax

To pass a 2D array to a function, you declare the function parameter with the number of columns fixed. The number of rows can be left unspecified.

• int arr[][COLS]: The 2D array parameter where COLS is the fixed number of columns.
• int rows: Usually passed separately to know how many rows the array has.

This tells the compiler how to access elements in memory correctly.

c

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

Example

This example shows how to define a 2D array, pass it to a function, and print its elements.

c

#include <stdio.h>

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

int main() {
    int myArray[2][3] = {{1, 2, 3}, {4, 5, 6}};
    printArray(myArray, 2);
    return 0;
}

Output

1 2 3 
4 5 6 

Common Pitfalls

Common mistakes when passing 2D arrays include:

• Not specifying the number of columns in the function parameter, which causes a compilation error.
• Confusing rows and columns sizes.
• Trying to pass a 2D array as int **arr, which does not work for true 2D arrays.

Always fix the column size in the function parameter.

c

/* Wrong way: missing column size */
// void printArray(int arr[][], int rows) { /* error */ }

/* Correct way: specify columns */
void printArray(int arr[][3], int rows) { /* ... */ }

Quick Reference

Concept	Example
Function parameter with fixed columns	void func(int arr[][4], int rows)
Passing array and rows	func(myArray, 3);
Access element inside function	arr[i][j]
Cannot omit column size	void func(int arr[][], int rows) // error
2D array declaration	int myArray[2][3];

Key Takeaways

Always specify the number of columns when passing a 2D array to a function in C.

Pass the number of rows separately to know the array size inside the function.

Do not use int** to represent a 2D array; it is not the same as int[][] in C.

Use nested loops to access elements inside the function using arr[i][j].