Why we pass arrays in functions parameter in C++

When writing code for a function you have three options for handling the data it is going to process :
1. The data is passed into the function.
2. The data is externally accessible meaning it can be global.
3 If the function is a method of a class the data can be a member of the class.

Because the function needs to process the data the array contains.

When you call a function, you pass it a copy of the parameter - this is called "pass by value".
In the case of an integer, a copy of the integer is passed:

int Double(int x) { return x * 2; }
...
int a = Double(666);
int b = Double(a);

The function doesn't to be changed to process the different results.

But what if I want to process an unknown number of integers? I can't write a different function for each possible number of parameters you might need - so we pass an array of integers instead:

int Sum (int arr[], int count)
   {
   int tot = 0;
   for (int i = 0; i < count; i++)
      {
      tot += arr[i];
      }
   return tot;
   }

Now I can call it with any array of integers I want:

int a[5] = {1, 2, 3, 4, 5};
int b[3] = {101; 201; 301};
int x = Sum(a, 5);
int y = Sum(b, 3);

Make sense?