Re^2: porting C code to Perl

Hello Mr. Muskrat and thanks for your reply,

> Perl's int is not the same as C's floor()..

I already admitted my superb ignorance but i read here that in C floor turns 1.6 1.2 2.8 2.3 into 1 1 2 2 or simply 'This function returns the largest integral value not greater than x'.

This is identical to the int function where any decimal are stripped out: say int $_ for qw(1.6 1.2 2.8 2.3)

> Perl has a pre-decrement just like C..

I have meditated a bit over this before trying to port the code and, sincerely I didnt read the C documents about post and pre increment, but as I have always understood the third part of the Perl's C style for loop is a statement on it's own: ie ++$var; or $var++; are identical.

Infact for($i=0;$i<4;$i++){say $i} and for($i=0;$i<4;++$i){say $i} produce the very same, expectable results. Switching between them in the above code does not change the result.

There are no rules, there are no thumbs..
Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.

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Re^3: porting C code to Perl (updated) by haukex (Archbishop) on Oct 23, 2017 at 20:08 UTC
the third part of the Perl's C style `for` loop is a statement on it's own: ie `++$var;` or `$var++;` are identical. Yes, that's correct, when they're written standalone as in `for(;;$var++)`. `++$var` vs. `$var++` only makes a difference when its return value is used: `++$var` will first increment the variable and then return the new value, while `$var++` will return the old value and then increment the variable. `$ perl -le 'for ( my $x=0; $x<3; print $x++ ) { }' 0 1 2 $ perl -le 'for ( my $x=0; $x<3; print ++$x ) { }' 1 2 3` [download] Update: In fact, note what Perl does here (edited for brevity): `$ perl -MO=Deparse -e 'for ( my $x=0; $x<3; print $x++ ) { }' for (my $x = 0; $x < 3; print $x++) { (); } $ perl -MO=Deparse -e 'for ( my $x=0; $x<3; print ++$x ) { }' for (my $x = 0; $x < 3; print ++$x) { (); } $ perl -MO=Deparse -e 'for ( my $x=0; $x<3; ++$x ) { }' for (my $x = 0; $x < 3; ++$x) { (); } $ perl -MO=Deparse -e 'for ( my $x=0; $x<3; $x++ ) { }' for (my $x = 0; $x < 3; ++$x) { (); }` [download]	[reply] [d/l] [select]
Re^3: porting C code to Perl by soonix (Chancellor) on Oct 23, 2017 at 20:31 UTC
For this particular use case, it doesn't matter, but with negative numbers, int and floor give different results (this is mentioned explicitly in the first link)	[reply]