Pass arrays to a function in C

In C programming, you can pass an entire array to functions. Before we learn that, let's see how you can pass individual elements of an array to functions.

Pass Individual Array Elements

Passing array elements to a function is similar to passing variables to a function.

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 have passed array parameters to the display() function in the same way we pass variables to a function.

// pass second and third elements to display()
display(ageArray[1], ageArray[2]);

We can see this in the function definition, where the function parameters are individual variables:

void display(int age1, int age2) {
  // code
}

Example 2: Pass Arrays to Functions

// Program to calculate the sum of array elements by passing to a function 

#include <stdio.h>
float calculateSum(float num[]);

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

  // num array is passed 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

To pass an entire array to a function, only the name of the array is passed as an argument.

result = calculateSum(num);

However, notice the use of [] in the function definition.

float calculateSum(float num[]) {
... ..
}

This informs the compiler that you are passing a one-dimensional array to the function.

Pass Multidimensional Arrays to a Function

To pass multidimensional arrays to a function, only the name of the array is passed to the function (similar to one-dimensional arrays).

Example 3: Pass two-dimensional arrays

#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 multi-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

Notice the parameter int num[2][2] in the function prototype and function definition:

// function prototype
void displayNumbers(int num[2][2]);

This signifies that the function takes a two-dimensional array as an argument. We can also pass arrays with more than 2 dimensions as a function argument.

When passing two-dimensional arrays, it is not mandatory to specify the number of rows in the array. However, the number of columns should always be specified.

For example,

void displayNumbers(int num[][2]) {
  // code
}

Recommended Reading: Call by Reference in C