Correct way to use short form of "if" in perl - perl

Question

I had written series of perl constructs using short form of if in perl as below,
( $psap[0] = sprintf( "%.4f", $psap[0] )
&& ( $psap[0] = "1:" . $psap[0] )
&& push( #all, $psap[0] ) )
if ( defined( $psap[0] ) );
( $psap[1] = sprintf( "%.4f", $psap[1] )
&& ( $psap[1] = "2:" . $psap[1] )
&& push( #all, $psap[1] ) )
if ( defined( $psap[1] ) );
I had faced some issues with this,
sprintf does not seems to be working ( Values are not rounded);
When I tried to print $psap[0] and $psap[1] value I was just getting 1 and 2 respectively and nothing else (#all contains the value of psap[0] as expected );
I agree that the code is not readable, I wanted some quick way to solve the issue that time. Later I wrote in full form of if which was working as expected.

Answer 1

Forget about the if... it's a red herring. Focus on this:
$psap[1] = sprintf( "%.4f", $psap[1] )
&& ( $psap[1] = "2:" . $psap[1] )
&& push( #all, $psap[1] )
That's essentially:
$psap[1] = X() && Y() && Z();
So you're setting $psap[1] to the result of a boolean && operation on three operands.
Either wrap your assignment in parentheses, like this:
( $psap[1] = sprintf("%.4f", $psap[1]) )
&& ( $psap[1] = "2:" . $psap[1] )
&& push( #all, $psap[1] )
Or use the low-precedence and operator:
$psap[1] = sprintf("%.4f", $psap[1])
and $psap[1] = "2:" . $psap[1]
and push(#all, $psap[1])

Answer 2

Your code is a dreadful misuse of the if statement modifier, which was never meant to control anything more than the simplest of statements.
I suggest you code it like this, which is far clearer
for my $i (0, 1) {
next unless defined $psap[$i];
$psap[$i] = sprintf '%d:%.4f', $i + 1, $psap[$i];
push #all, $psap[$i];
}

Answer 3

Logical operators should be avoided if you don't really want to depend on their result, and just want to sequentially execute your code, thus
$psap[1] = sprintf("%.4f", $psap[1]), $psap[1] ="2:$psap[1]", push(#all, $psap[1])
if defined $psap[1];
or shorter,
defined and $_ = sprintf("%.4f", $_), $_ ="2:$_", push(#all, $_)
for $psap[1];
or shorter,
defined and $_ = sprintf("2:%.4f", $_), push(#all, $_)
for $psap[1];

Answer 4

The assignment to $psap[0] is of lower precedence than the &&, so it is being assigned the value of
sprintf( "%.4f", $psap[0] ) && ( $psap[0] = "1:" . $psap[0] ) && push( #all, $psap[0] )
Just wrap it in some extra parentheses:
#!/usr/bin/env perl
use strict;
use warnings;
my #psap = ( 0.123456789 );
my #all;
( ( $psap[0] = sprintf( "1:%.4f", $psap[0] ) )
&& push( #all, $psap[0] )
)
if ( defined( $psap[0] ) );
print $psap[0], "\n";
I also took the liberty of putting the "1:" into the sprintf rather than building the string in two steps.
As shown in the operator precedence and associativity table, and is of a much lower precedence and could be used instead:
$psap[0] = sprintf( "1:%.4f", $psap[0] ) and push( #all, $psap[0] )
if ( defined( $psap[0] ) );
output:
1:0.1235