% gradeCalculator.m   P. Conrad, demo for CISC106 Fall 2006
% input a sequence of grades (all out of 100) and calculate the average


% *** Print welcome, and instructions to the user ***

fprintf('Welcome to the grade averager.  If you\n');
fprintf('input a sequence of grades, I can compute the average.\n');
fprintf('\n');
fprintf('I''ll ask for grades one at a time.\n');
fprintf('  * First I''ll ask you for a title for each grade (e.g. "hwk1")\n');
fprintf('  * Then I''ll ask for the score out of 100 points\n');
fprintf('  * Enter "done" for the title when you are finished\n');
fprintf('\n');

% **** set up variables

grades = [];  % an empty array at first; this will store all the grades
count = 0;    % this variable will count how many grades there are

% **** Main loop to accumulate grades

% Note the pattern: ask for input before the while loop, and at the 
% _bottom_ of the while loop.   See this pattern too, on p. 150-151 of
% Chapman textbook (MATLAB Programming for Engineers, 3rd Edition).

title = input('Enter a title for this grade (or "done" when finished): ','s');
while (title ~= 'done')
  % ask user for a grade
  
  prompt = ['Enter a grade out of 100 points for ' title ': '];
  thisGrade = input(prompt);
  
  count = count + 1;
  grades(count)  =  thisGrade;
  
  title = ...
      input('Enter a title for this grade (or "done" when finished): ','s');
end

% Use a for loop to accumulate the sum (* see note at end of program)

sum = 0;
for (k = 1:count)
  sum = sum + grades(k);
end

average = sum / count;

fprintf('The average of your %d grades is %5.1f\n',count,average);



% *Note: We could have accumulated the sum inside the while loop that reads
%  in the data instead of doing it in a separate for loop.   I did it 
%  separately only because this program is intended to "teach" about
%  while loops and for loops.
%
%  The idea is that, in general, while loops are used when
%    * you don't know in advance how many times the loop will run, but
%    * you DO know what the "stopping condition" is.
%    * you express the loops as "while ( stopping condition is not true) 
%
%  You use a for loop when 
%    * you have a definite idea of how many times the loop is to be done
%    * you have an index variable that counts up through various values
%
%  Also note: since this is a programming course, and not _just_ a MATLAB
%  course, when there is more than one way to accomplish something, I'll
%  generally prefer to teach the way that translates more easily into
%  other programming languages.  For example, in this program:
%
%    grades(count)  =  thisGrade;
%
%  could be replaced with:
%
%    grades = [ grades thisGrade ];
%
%  but the first way translates easily into C, C++ and Java, while the
%  second way is pretty specific to MATLAB.   So, I'll tend to teach you
%  the first way more often.