16. Passing Arrays to Functions

C++ does not allow passing an entire array as an argument to a function. However, You can pass a pointer to an array by specifying the array’s name without an index.

If you want to pass a single-dimension array as an argument in a function, you would have to declare function formal parameter in one of following three ways and all three declaration methods produce similar results because each tells the compiler that an integer pointer is going to be received.

Way-1

Formal parameters as a pointer as follows −

void myFunction(int *param) {
   .
   .
   .
}

Way-2

Formal parameters as a sized array as follows −

void myFunction(int param[10]) {
   .
   .
   .
}

Way-3

Formal parameters as an unsized array as follows −

void myFunction(int param[]) {
   .
   .
   .
}

Now, consider the following function, which will take an array as an argument along with another argument, and based on the passed arguments, it will return average of the numbers passed through the array as follows −

double getAverage(int arr[], int size) {
  int i, sum = 0;       
  double avg;          

   for (i = 0; i < size; ++i) {
      sum += arr[i];
   }
   avg = double(sum) / size;

   return avg;
}

Example

Now, let us call the above function as follows −

#include <iostream>
using namespace std;
 
// function declaration:
double getAverage(int arr[], int size);

int main () {
   // an int array with 5 elements.
   int balance[5] = {1000, 2, 3, 17, 50};
   double avg;

   // pass pointer to the array as an argument.
   avg = getAverage( balance, 5 ) ;
 
   // output the returned value 
   cout << "Average value is: " << avg << endl; 
    
   return 0;
}

When the above code is compiled together and executed, it produces the following result −

Average value is: 214.4

As you can see, the length of the array doesn’t matter as far as the function is concerned because C++ performs no bounds checking for the formal parameters.