Arrays and Functions

Things to note about C-style arrays:
- An array is not a type
- An array is a primitive C-style construct that consists of many items stored consecutively and accessed through a single variable name (and indexing)
- This is actually done by remembering the starting address of an array, and computing an offset
- The name of an array acts as a special kind of variable -- a pointer -- which stores the starting address of the array
An array can be passed into a function as a parameter
- Because an array is not a single item, the array contents are not passed "by value" as we are used to with normal variables
  - The normal meaning of "pass by value" is that the actual argument value is copied into a local formal parameter variable
  - In the case of arrays, just the pointer is copied as a parameter. We'll see this in more detail when we get to pointers
- When an array is sent into a function, only its starting address is really sent
- This means the function will always have access to the actual array sent in
- Returning an array from a function works similarly, but we need pointers to use them well (not yet covered)
Example function:
```
  void PrintArray (int arr[], int size)
  {
    int i;
    for (i = 0; i < size; i++)
      printf("%d ", arr[i]);
  }
```
Note that:
- The varibale arr acts as the local array name inside the function
- There is no number in the brackets. int [] indicates that this is an array parameter, for an array of type int
- It's usually a good idea to pass in the array size as well, as another parameter. This helps make a function work for any size array

Sample call to the above function:

  int list[5] = {2, 4, 6, 8, 10};

  PrintArray(list, 5);		// will print: 2 4 6 8 10

Using `const` with array parameters

Remember: When passing an array into a function, the function will have access to the contents of the original array!
Some functions that should change the original array:
- Sort(), Reverse(), SwapElements()
What if there are functions that should not alter the array contents?
- PrintArray(), Sum(), Average()
Put const in front of the array parameter to guarantee that the array contents will not be changed by the function:
```
  void PrintArray (const int arr[], const int size)
  {
    int i;
    for (i = 0; i < size; i++)
      printf("%d ", arr[i]);
  }
```
Notice that the const on the variable size is a good idea in this example, too. Why?

arrayfunc.c -- Here's an example program illustrating a couple of functions that take array parameters.

Practice exercises

Try writing the following functions (each takes in one or more arrays as a parameter) for practice:

A function called Sum that takes in an array of type double and returns the sum of its elements
A function called Average that takes in an integer array and returns the average of it's elements (as a double)
A function called Reverse that takes in an array (any type) and reverses its contents
A function called Sort that takes in an array of integers and sorts its contents in ascending order
A function called Minimum that takes in an array of type double and returns the smallest number in the array

Arrays and Functions

Using const with array parameters

Practice exercises

arrayfunc2.c -- Example written up in lecture class. Examples of minimum and maximum functions, as well as Selection Sort

Using `const` with array parameters