CISC181 Midterm 2, 06S, Post-Exam Notes

These notes are here to help you understand what you missed on the exam, and to provide at least a partial rubric for how it was graded.

The complete exam (with answer key) is available online—however, in that document, question 10 is formatted differently than it was on the actual exam. This web page shows how it was actually formatted.

Questions 1-9

These questions were multiple choice. The median score was 26/30, meaning that half the class scored a B+ or higher. Furthermore, only 10 students scored lower than 21/30 (i.e. less than a C-). The answers are posted online, so I'm not going to add any detailed comments here.

Question 10

This question was a two-page 11 x 17 foldout sheet. The images below show correct answers. These are scans from actual exam papers of students with perfect scores on this question. There were at least* seven such papers.

(*I have not yet graded the papers of those not putting their section number on page one.)

Part a, b: idempotent header files, and function prototypes for get functions

(a) making the #include file idempotent.

Sample deductions:

• (-1) misspelling #ifndef or #define (e.g. all of these are wrong: #def, #indef, #ifendif)
• (-2) leaving out the second line (the #define line)
• (-5) a completely wrong or irrelevant answer (e.g. #include <iostream>)

(b) function prototypes for the get functions

Sample deductions:

• (-1) Failure to use const on get functions. Get functions should always be declared as const as a matter of good programming style.
• (-2) Not making the get functions void. Get functions don't need any parameters—they are invoked on an object that already has the data members inside of it. You just return their values.
• (-1 each) incorrect return types. A get function cannot be void—its return type needs to match that of the value being returned.

 

Part c,d,e: member function definitions

(c) function definitions for the get functions

Sample deductions:

• (-10) missing or completely wrong answer (e.g. doing cin >> and cout <<, which has no place inside a get function), and not even including the name of the class and the binary scope resolution operator. If you had everything else wrong, but at least got the class name and binary scope resolution operator correct, you got (-8) instead of (-10).
• (-1 each) incorrect return type on function
• (-2) forgetting the class name and the binary scope resolution operator (TempReading_C::) which must always precede the name of the function when defining member functions outside the class declaration.
• (-2 each) returning the wrong thing—e.g. returning a parameter passed in, instead of the private data member.
  • Note: I did not make a second deduction for having formal parmeters if I already deducted for that in (b), unless the syntax of the formal parameter was incorrect.)
• I did not make a second deduction for failure to use const on get functions, if I already deducted for that on (b). However, get functions should always be declared as const as a matter of good programming style, and in the future I might not apply a "no double jeopardy" rule.

(d,e) the body of the function definitions for the set functions

Sample deductions:

• (-1 each) doing return (0); on a void function (just return; is ok, or leaving off the return; is ok too.)
• (-1) misspelling a variable, or using the wrong case (e.g. Temp instead of temp)
• (-2 each) declaring a data member as a local variable, e.g.
  double temp = theTemp; instead of
temp = theTemp;
  This is not acceptable because declaring temp as a local variable hides the private data member, which will remain unassigned. Doing
  double temp = theTemp;
  assigns a value to a local variable on the stack that disappears as soon as you return from the member function!
• (-4) a completely wrong or irrelevant answer (e.g. getroom(room); or return(theTemp); )

Part f, g, h: using classes in a main program

(f) doing a #include on the header file

Sample deductions:

• (-2) if you did a #include on tempReading.cc instead of tempReading.h
• (-4) Completely wrong answer (e.g. doing a #include on some file that wasn't even in the question, or writing down something else irrelevant.)

(g) invoking the two setter methods

You needed to inoke the setter methods on the object t. Some sample deductions:

• (-2) Invoking the constructor on t again, but passing in temp and room. This won't compile, because you can't redefine t.
• (-2) Forgetting to do t. in front of the function calls (member functions have to be invoked on an object using dot-notation, unless they are declared static.)
• (-3) Completely mucking up the syntax
• (-4) Completely wrong answer

 

(h) invoking the constructor on x, but passing in temp and room

Some sample deductions:

• (-2) passing in something other than temp and room
• (-2) using t instead of x, or leaving out x completely
• (-4) Completely wrong answer

Part i, j: compiling C++ classes with Makefiles

(i) defining the CCC variable

Sample deductions:

• (-1) putting quotes around CC or g++
• (-1) using C++ style comment, e.g. // define compiler
  instead of Makefile style comment, e.g. #define compiler
• (-2) defining CCC as gcc instead of either CC or g++

(c) defining the line in the Makefile that links

Sample deductions:

• (-4) completely incorrect answer
• (-2) messing up the part that should be either -o testTempReading or -o $@

Question 11

Question 11 involved type expressions. Most students did well here—at the time I am writing this, I only have data for those students that put their section number on page 1 of their exam, but among those students, half scored an 18/20 or higher, and three-quarters scored a 14/20 (i.e. a C-) or higher. Therefore, I'm not going to go over this part in detail—the answers are online, and there are a large number of practice problems online as well.