Re: Simple question!
See in-line below....
"Bo Persson" <bop@gmb.dk> wrote in message
news:4hhd1eF1rqoqtU1@individual.net...
"Alex Blekhman" <xfkt@oohay.moc> skrev i meddelandet
news:OFi00NLpGHA.516@TK2MSFTNGP05.phx.gbl...
I can see that many attribute some inherently evil properties to
`goto' statement. Michael K. O'Neill already posted good article in
this thread. I'd second his opinion. There is nothing wrong with
`goto' per se. All of us have seen horrible code without single
`goto'. This is not that `goto' (or any other language construct)
that makes code bad; it's quite the opposite: bad, stupid coders
produce filthy code (no matter what the language the use for that).
Any feature in a programming language is just a tool. Use it wisely
and you'll get beautiful elegant code. I just can't get all these
rumbles about `goto'.
Because it is an inherently unstructured way to get from one arbitary
point in the program to another? :-)
When 99.9% of the uses are bad, the general advise to students is:
"Don't use it"!
Frank Rubin is simply wrong! Even though he has found the break
statement, he doesn't see how to use it to avoid the goto.
His Pascal code:
for i := 1 to n
do begin
for j :=1 to n do
if x[i, j] <> 0 then
goto reject;
writeln('The first all-zero row is ', i);
break;
reject: end;
could easily have been written (C++ style, 0 based array):
bool is_all_zero_row(int row)
{
for (int col = 0; col != n; ++col)
if (x[row][col] != 0)
return false;
return true;
}
// ...
for (int i = 0; i < n; ++i)
{
if (is_all_zero_row(i))
{
std::cout << "The first all-zero row is " << i << std::endl;
break;
}
}
See Ma, no gotos !
One of the central premises of Dijkstra's structured programming concepts
was that each block of code should have exactly one entry point and exactly
one exit point. The reason for this requirement related to flow control and
proofs of correctness.
The "ban" on goto's is an offshoot of this "one entry/one exit" requirement.
Your example, which uses multiple "returns" to exit from multiple different
places in the is_all_zero_row() function, manifestly violates this "one
entry/one exit" requirement of structured programming. It's simply not
properly structured from a "structured programming" perspective. In fact,
if you think about it, multiple "returns" is the full moral equivalent of
goto statements, and should be avoided for exactly the same reasons.
Other constructs, such as "break" and "continue", suffer from the same
problem.
Frank Rubin's article recognized this. The code that uses "break" also uses
"goto", and Rubin recognizes that such code is not "structured". On the
other hand, the goto-less code also does not use any "breaks" or
"continues", and exactly follows the "one entry/one exit" requirement.
As others have pointed out before, having to break out of multiple
loop levels is a good indication that the code can be refactored.
Having an is_all_zero_row attribute for the matrix seems like a good
idea, if that is an important property of x.
Bo Persson