Write C++ code for each of the following: a) Write a function call average that will accept an array of type double. It should take the average of all the numbers in the array and return the average to the calling program. Be sure to include all needed parameters. Write a function call to call the function average. Declare any needed variables. Write a loop that will ask the user for all the values in the array before calling the function. b) c) Write a prototype for the function written in part a