Who modified my local variable?

Michael L Torrie torriem at chem.byu.edu
Tue Jun 13 14:10:23 MDT 2006

On Tue, 2006-06-13 at 14:03 -0600, Nicholas Leippe wrote:
> On Tuesday 13 June 2006 13:11, Michael L Torrie wrote:
> > Sure.  But my real point was the Java habit of always doing "new" causes
> > a ton of problems for Java programmers heading into C++.  Rather than
> > use a local variable allocated on the stack, they do "new" which leaks.
> > That is the problem.  So really it's not a language problem; it's a
> > programmer problem.  But a programmer can be trained; unfortunately Java
> > is not a good trainer in this instance.  In my opinion it would be
> > better to subject a new CS student to C and C++ in all their glory and
> > then introduce them to managed, Garbage-collected languages later,
> > rather than the other way around.
> Hrm. Maybe. But, silent show of hands, how many plugger's first programming 
> language was some dialect of BASIC?

Unfortunately, I did learn applesoft BASIC and Microsoft's BASIC.
Fortunately at a very young age I was introduced to Borland's TurboBASIC
compiler (later became PowerBASIC) which was more like Pascal than
GWBASIC.  (What's a line number?).  User-defined functions, Switch
statements, If blocks, etc.  Was wonderful.

> The key concepts are dynamic allocation, and variable binding.  Each can be 
> separated, and can be taught better in some languages than others.

Right. Scheme or LISP is the best.

> Some forms of BASIC implement neither concept.  Every variable is in fact 'the 
> variable', and there is no dynamic allocation (save for variable sized, 
> global arrays).
> This is where I started.  Then, I went straight to assembly language, and then 
> to C++.  Having a good grasp of what is occurring physically in hardware 
> (asm) made understanding pointers trivial.  To understand references, IMO, 
> implement a compiler (or take a compiler course), and you'll have no more 
> confusion--it's all about symbol tables.


> The real learning issues come about when different parts of these two concepts 
> have overlapping syntax across languages.
> IMO, better to introduce language concepts w/o dynamic memory management 
> first, then memory management and variable bindings as two distinct (though 
> interdependent) topics later.
> You can teach dynamic memory management in subtle ways w/o it.  For example, 
> teach linked lists, but implement them using arrays.  Then when you introduce 
> pointers--tahdah!--the student already understands exactly what is happening.  
> The storage location has moved from the array he explicitly declared to an 
> intrinsic property of the computer, and now, in his mind, the pointer is no 
> different from the array index variable he had to use before.

Unfortunately that's not the way most CS students are taught.  Tis sad.


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