When else is used after two nested ifs without block delimiters (curly braces),
one may mismatch the else statement with the if preposition.
It is better to always use curly braces.
Example
Error prone
if ($a == 0)
if($c > 0)
print "OK";
else
print "a is not zero!";
Recommended
if ($a == 0) {
if($c > 0) {
print "OK";
} else {
print "a is not zero!";
}
}