This homework is due on Friday, 2/28/14 by 2:30pm. Your script should
be named handin3 

Be sure to demonstrate at least the sample input below to receive full
credit (but be aware you should show at least one other branch of your
code for full credit as well). Do not forget to cat your file, compile
your source or run your samples.

In this homework you will write functions and explore function calls.


Step 1: Write a function that gets user input for 3 grades as real
numbers. These values are expected to be between 0 and 100. Perform
some error correction if the user inputs a negative value. (This can
be a while loop or an if statement, but be sure to handle this case).

Step 2: Write a function that computes the average of 3 real numbers
and returns the result. There is no cout or cin allowed in this
function.

Step 3: Write a function that outputs a letter grade corresponding to
real number input. Use the usual metric (90-100 is an A, 80-90 is a B
and so on).

Given these three functions, you should be able to use this main (assuming you name your functions similarly).

int main() {

    string user="yes";
    while(user == "yes") {
         float x,y,z, avg;
	 getGrades(x,y,z);
	 avg = computeAverage(x,y,z);
	 reportGrade(avg);
	 cout << "Type 'yes' to compute another: ";
	 cin >> user;
    }


}
    
Sample input:
100 100 100
yes
50 50 50
yes
100 50 100
no


Sample output (based on the input above):

Please input 3 grades:  
Your final average is: A
Type 'yes' to compute another:
Please input 3 grades:
Your final average is: F
Type 'yes' to compute another:
Please input 3 grades:
Your final average is: B
Type 'yes' to compute another:
Goodbye!