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.

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Pass Individual Array Elements

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

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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
}

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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.