Why new programming students aren't fairing well.

It has amazed me how poorly prepared students are for the more advanced programming classes I've taken, but recently I've had to go back and take a basic C course for my degree. Now I know why.

I thought I'd share some of my instructor's thoughts on C with you all.

1.

Code:

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int b = 5;

-b++ //will evaluate to -6 AND b will have -6 as its value after the expression

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2.

Code:

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(a + b)++  //is apparently a valid expression

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3. Any variable declared in main() is in scope in any function if it is written below main.

4. Functions should never return anything but exit status. Goodbye float, char, pointer, struct, etc. functions. And 0 means no error.

5. Formal parameters in a function definition are not local variables to that function, they are merely aliases to the actual parameters. They produce no overhead in other words. (Yay for infinite recursion).

6. For loops are counting loops, while and do/while are conditional. For loops are more efficient because of this.

7. Never, ever, ever use break or continue. ( I'm sure there are others who feel the same way on this ).

More to come, I'm sure. Sadly, after 10 weeks, the class has seen probably 30 lines of code all told.

Quote:

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Originally Posted by Tclausex

1.

Code:

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int b = 5;

-b++ //will evaluate to -6 AND b will have -6 as its value after the expression

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I would not guess that this would be the result; I would guess +6 in b.

Quote:

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Originally Posted by Tclausex

2.

Code:

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(a + b)++  //is apparently a valid expression

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IMHO, This is maybe true; No idea how it is useful.

Quote:

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Originally Posted by Tclausex

3. Any variable declared in main() is in scope in any function if it is written below main.

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IMHO, This is completely false.

Quote:

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Originally Posted by Tclausex

4. Functions should never return anything but exit status. Goodbye float, char, pointer, struct, etc. functions. And 0 means no error.

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I have heard this one below from non-C programmers; it has it pluses and minus. I think it does NOT really work well for a low level Language like C.

Quote:

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Originally Posted by Tclausex

5. Formal parameters in a function definition are not local variables to that function, they are merely aliases to the actual parameters. They produce no overhead in other words. (Yay for infinite recursion).

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The conclusion is defiantly wrong in my opinion (true for inline functions.)
The parameters are passed on the stack on most; maybe all implementations.

Quote:

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Originally Posted by Tclausex

6. For loops are counting loops, while and do/while are conditional. For loops are more efficient because of this.

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I will give him this one; I think it might be right.

Quote:

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Originally Posted by Tclausex

7. Never, ever, ever use break or continue. ( I'm sure there are others who feel the same way on this ).

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I assume from number 7 that the switch/case statement is NOT allowed to be used.


At my College, an good (according to every body I asked) instructor in C never gets to covering how to write a proper header in C in the first semester.

I have reached the conclusion that there is NO instructor that really teaches the basic of programming very well at my College; they all appear to teach the language syntax instead of how to break the problem down into steps. Note: The good instructor in C seems to be the closest to teaching how to program; but, he runs out of time to teach the full beginners level of C programming.


Tim S.

Quote:

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Originally Posted by Tclausex

Sadly, after 10 weeks, the class has seen probably 30 lines of code all told.

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I'm not surprised:

Quote:

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Originally Posted by Tclausex

Code:

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(a + b)++  //is apparently a valid expression

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...

3. Any variable declared in main() is in scope in any function if it is written below main.

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...since the above two will lead to a lot of code that even the most absurdly lenient C compilers from 1980 wouldn't know what to do with.

I've met exactly one person like that in my programming career - thankfully for me, he didn't know enough programming to know I'd totally ignored his "guidelines". The code worked (despite his best efforts) so he didn't care to learn too much...

I go to University of Central Florida which has one of the highest rated CS and Engineering departments in the country. I believe it's like #5 or so. Even so, the teachers do quite well at teaching but you have to do a lot of outside work in order to fully understand the concepts. Relying on teacher for sufficient knowledge is silly nowadays.

There was a teacher in my high school who taught C++ or, as his website put it, "C." He gave all his students a copy of Turbo C++ 2.x (or so) for DOS through 2007-ish when he upgraded to 4.0. It was a 5 day/week, 2 hour/day class that ran yearlong but never covered arrays or pointers or namespaces or templates or type (ie. class) definition.

The class may have just been axed this year, I'm not sure.

-b++ evals to -6 but 6 is stored in b. ++ has higher precedence than unary minus.

Seeing as how for is really just a preprocessor directive that expands to a while loop, I'd say they're equally efficient.

Your professor might be retarded.

Quote:

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Originally Posted by Epy

Seeing as how for is really just a preprocessor directive that expands to a while loop, I'd say they're equally efficient.

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If you mean a for loop could be imitated using a macro that expands to a while loop, I'd agree. But the the keyword for itself is definitely unrelated to the preprocessor.

Well,

-b++ evaluates to -5.
(a + b)++ would be akin to saying (a + b) = (a + b) + 1, which makes no sense at all. Increment/decrement operators require 1 lvalue. Also, it was being used on the board as an example of adding 1 to the evaluation of a plus b, which has to be the ultimate in laziness.

And as far as I've ever understood it, a for() loop is just another loop. To say that it isn't conditional, is absurd. Unless you write it as for( ; ; ) of course, but then it's infinite unless you put a conditional inside! Whether it's more efficient or not, I couldn't say. If someone out here understands what's going on under the hood would like to comment on that, I'd love to know.

Quote:

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Originally Posted by Tclausex

It has amazed me how poorly prepared students are for the more advanced programming classes I've taken, but recently I've had to go back and take a basic C course for my degree. Now I know why.

I thought I'd share some of my instructor's thoughts on C with you all.

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And on the other hand, we have people here who were struggling to write what I would consider a commercial quality application as their second assignment in first semester...

One has to wonder how many programmers know how to teach and how many teachers actually know how to program.

Out of curiosity, but about the -b++ and (a + b)++ examples: was there no student in the class who attempted the examples and then asked the teacher why the result was different or why the program would not compile?

#4 and #7 are stylistic issues, so pure beginners cannot be expected to know better (and #7 may be held by the "bondage and discipline" variety of experienced programmers). Until it occurs to a beginner that he/she needs to modify a variable in a function such that the result is reflected in the caller, #5 could well appear correct too, efficiency issues aside.

As a rule of thumb of "counting" versus "generic condition", #6 could be useful to help a beginner choose, except for the claim about efficiency, which would be beyond a beginner's ability to dispute anyway.

Quote:

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Originally Posted by mdj441

If you mean a for loop could be imitated using a macro that expands to a while loop, I'd agree. But the the keyword for itself is definitely unrelated to the preprocessor.

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I'm having trouble finding a solid source, but you will see several discussion results that say most compilers expand for loops to while loops (not necessarily using the preprocessor, no). This is what I was referring to.

And regarding -b++ evaluating to -5: goddamn prefix and postfix increments. b is indeed 6, but you're right, that expression does evaluate to -5.

Code:

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int b=5;
-b++;
printf("b equals: %d",b);

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b equals: 6

In Pelles C.

Quote:

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Originally Posted by Adak

b equals: 6

In Pelles C.

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When compiled by any standard conforming C compiler.

Quote:

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Originally Posted by Epy

I'm having trouble finding a solid source, but you will see several discussion results that say most compilers expand for loops to while loops (not necessarily using the preprocessor, no). This is what I was referring to.

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This is wrong. Hopefully you just misunderstood and they were saying that you can code any while loop as a for loop or vice versa, but what you've described above is not how compilers work.

Quote:

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Originally Posted by Adak

Code:

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int b=5;
-b++;
printf("b equals: %d",b);

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b equals: 6

In Pelles C.

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If you're replying to what I said, you should note that I said that b is 6 but that expression evaluates to -5. i.e.

Code:

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int result, b = 5;
result = -b++;
printf("%d\n%d\n", result, b); // prints -5 and 6, respectively

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Quote:

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Originally Posted by KCfromNC

This is wrong. Hopefully you just misunderstood and they were saying that you can code any while loop as a for loop or vice versa, but what you've described above is not how compilers work.

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I'm going to go with this is a common misconception then. I've heard it a few times before, and for instance this article:

c - Example of a while loop that cannot be replaced by a for loop - Stack Overflow

Someone clearly says "Most compilers actually expand for loops to while loops", which doesn't really leave it open for interpretation. This doesn't mean that what he said is correct, but do you have supporting evidence?

Quote:

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Originally Posted by Epy

Someone clearly says "Most compilers actually expand for loops to while loops", which doesn't really leave it open for interpretation. This doesn't mean that what he said is correct, but do you have supporting evidence?

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Supporting evidence would be that compilers usually translate to some intermediate language and work with that, so any "expand some type of loop to another type of loop" would be in terms of that intermediate language, not C, and it may just involve goto or an equivalent, not specific loop constructs.

Thanks Epy, that cleared it up.

I don't know why I even brought up the thing about the for loops. Pretty much all loops end up using the jump if something instruction (jne, jle, whatever), right?

Edit: point is, it basically ends up being the same machine code in the end, how can for loops be more efficient than while loops? There's always some sort of conditional that's executed every iteration of the loop.

Quote:

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Originally Posted by Epy

I don't know why I even brought up the thing about the for loops. Pretty much all loops end up using the jump if something instruction (jne, jle, whatever), right?

Edit: point is, it basically ends up being the same machine code in the end, how can for loops be more efficient than while loops? There's always some sort of conditional that's executed every iteration of the loop.

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A for-loop communicates intent. Both to other programmers and to the compiler itself. It only takes 10 minutes of fooling with the compiler to see that in some cases it generates different code depending how you write a loop. Whether this is just happenstance or indicates something deliberate inside the compiler, I don't know. It's true that everything compiles to some intermediate format which is where most optimizations happen, there's nothing that says the compiler can't take advantage of additional information if it wants to.

For instance, in some big complex while-loop it may be unclear which variable plays the role of indexer. In a for-loop it is usually very obvious which variable is the indexer.

Quote:

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Originally Posted by Tclausex

It has amazed me how poorly prepared students are for the more advanced programming classes I've taken, but recently I've had to go back and take a basic C course for my degree. Now I know why.

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Wow. That is very scary stuff. You should complain to someone.... there are enough plain WRONG points there.

Quote:

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Originally Posted by Tclausex

7. Never, ever, ever use break or continue. ( I'm sure there are others who feel the same way on this ).

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Heh - I remember my supervisor at university saying that to me too. Well, not "never ever ever", but "break and continue are bad!". I asked him why, he said that it is difficult to formally prove correctness of a loop with breaks/continues. I don't know if that's widely true or if it was just true of the particular methods he was using.
I suppose then that "never, ever, ever use break or continue" might be good advice if you were working on a safety critical system where code needed to be proven.

"Never ever ever use goto", I'll stand by :)

Quote:

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Originally Posted by smokeyangel

Heh - I remember my supervisor at university saying that to me too. Well, not "never ever ever", but "break and continue are bad!". I asked him why, he said that it is difficult to formally prove correctness of a loop with breaks/continues. I don't know if that's widely true or if it was just true of the particular methods he was using.
I suppose then that "never, ever, ever use break or continue" might be good advice if you were working on a safety critical system where code needed to be proven.

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Most normal uses of break/continue can easily be rewritten to not use them. They're meant to allow you to write clearer code, not to enable you to do things you couldn't otherwise do. There are probably cases where break/continue is the only way to accomplish a certain control flow, but I can't imagine them, and it's usually possible to transform a piece of code that uses them into a piece of code that doesn't.

For instance, a loop like this:

Code:

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for (...)
{
    foo();
    if (bar())
        break;
    baz();
}

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Can be replaced with this:

Code:

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bool fBar = false;
for (...)
{
    if (!fBar)
    {
        foo();
        if (bar())
            fBar = true;
        else
            baz();
    }
}

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It's inefficient, more difficult to read, but it does not use break. But I'd question the sanity of somebody who told me the second loop is easier to analyze than the first.

Your replacement isn't correct, brewbuck, as it doesn't terminate the loop. You probably intended something like

Code:

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bool fBar = false;
for (!fBar && ...)
{
        foo();
        if (bar())
            fBar = true;
        else
            baz();
}

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All 1 to 7 are all very wrong. No surprise there, as that's the whole reason Tclausex posted them.

1, 2, 3, and 5 can be disproven using an appropriate code sample.
4 Disagrees with a decent percentage of standard library functions.
6 can be disproved using an appropriate compiler. Alternatively one can take the stance that for is not more efficient than do..while because they are not interchangeable.
7 If I catch anyone avoiding an appropriate use of break and instead inserting a dumb flag variable then they get a flogging.

To be perfectly fair, most schools start the basic programming with Java.

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Originally Posted by Strahd

To be perfectly fair, most schools start the basic programming with Java.

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The Perils of JavaSchools - Joel on Software

We have to take multiple C classes before we can take upper level Programming classes that include other languages. There is an intro to OOP with Java but you have to take the first C course first. I'm glad it's this way at my uni.

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Originally Posted by manasij7479

The Perils of JavaSchools - Joel on Software

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Now now I do agree, when I said "start out with java" I meant as the first basic intro to programming class.

Some schools I've seen it goes

Intro (java)

Intermed (java)
Data Struct (C)

Large Programs (Java)
Intro to Computing Systems (Assembly)

And they hit other langs, like VHDL, MATLAB, SCHEME, etc during the progress.

Appalling that CS students are even exposed to MATLAB. Fortran is a mans language when it comes to numerical computing.

Quote:

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Originally Posted by Epy

Appalling that CS students are even exposed to MATLAB. Fortran is a mans language when it comes to numerical computing.

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Contrary to popular belief, there are some female CS students, and thankfully I got to meet some of them :)