Problem Statement:  Write a program to calculate the average of three test scores and print a
relevant evaluation notice.  Assume the test scores are whole numbers <= 100. If any score
is negative, say "Invalid Data: Score(s) less than zero".  Display the average score, and if the
average is >= 70 say "Passing".  If the average >= 60 and < 70 say "Passing but marginal" and
if the average is < 60 say "Failing."

Example Test Plan

Student Joe Student
Program Notices
No. Description Input Data Expected Output
1 Verify prompt, echo input, and output messages.   Enter a Student ID number and three test scores:
    1 100 100 100 Student number: 1

Test Scores: 100, 100, 100
      Average score is 100.00--Passing.
2 Valid data

Marginal score

2 60 60 63 61 Passing but marginal
3 Failing score 3 50 50 50 50 Failing
4 Invalid data

1st item

 4 -50 50 50 Invalid Data: Score(s) less than zero
5 2nd item 5 50 -50 50 Invalid Data: " " " "
6 3rd item 6 50 50 -50 Invalid Data: " " " "
7 Verify Calculations 7 70 80 85 70+80+85 / 3 = 235 / 3 =

78.333
8 Boundary conditions

above Pass

 8 70 70 70 70.0 Passing
9 below Pass 9 69 69 69 69.0 Passing but marginal
10 above Fail 10 60 60 60 60.0 Passing but marginal
11 below Fail 11 59 59 59 59.0 Failing