Question

Why do I get a different output with $key++ and $key+1?

What should I do to refer to the next element in the loop using foreach?

foreach($diff as $key=>$val) {

if(in_array($diff[$key],$common) && in_array($diff[$key+1],$common)) {}

if(in_array($diff[$key],$common) && in_array($diff[$key++],$common)) {}

}

Answer 1

$x++ returns the old value of $x (before the increment). For example, $x=3; print $x++; will print “3”. It also modifies $x, so it’s not the best choice unless that’s your intent. (Here, incrementing would be pretty useless, particularly since the modified keys never see the outside of the loop.)

++$x would return the new value of $x. Like $x++, though, it’s semantically wrong for just getting the next number, as it modifies $x.

Just stick with $x + 1.