PHP and Logical math??

deep

Hello,

I made a discovery earlier today... i think...

You see, in math there is a sign for negation and in programming that sign is (!). Logical mathematics say that

!true = false
!false = true

But writing this in php will do this...


if(!true){
   echo "...returns false."; //echo not printed
}
if(!false){
   echo "...returns true"; //echo printed!?!?
}

In mathematical tearms the second if-statement is correct BUT i have heard that if you write (!) in a if-statement like below then the if-statement only looks for false values?


$test = true;
if(!test){
   echo "...returns false."; //echo not printed
}

This will not print the echo because the (!) sign only looks for false values in the if-statement? But changing $test to false will return true... should it? Im a little confused...

drawmack

You said it yourself !TRUE = FALSE. If statement use boolean math. When you say if (whatever) {} the code inside the {} will only execute if whatever is true. When you say if(!whatever) {} the code inside the {} will only execute when whatever is false, becuase you're flipping it, thereby making false true and true false.

This is confusing and that is why the ! operator should be used sparingly as most.

MarkR

Firstly, you made an error and did

if (!test) {

Rather than

if (! $test) {

Which is, I suspect, what you meant.

Secondly, you have to understand what PHP's definition of being true is.

If you attempt to apply a boolean operator to something or use it in a boolean context, PHP will implicitly cast it into a boolean.

This means, basically speaking,

Any number other than 0 is considered true
Any string which is not the empty string is considered true
Any object or resource (I think) is considered true
Null or an undefined value are considered false

The PHP docs can help you here. This may not be what you expect, specifically, the string "false" will of course be considered true.

You should enable warnings ALL THE TIME, ideally triggering fatal errors. Bareword warnings are usually the result of a programming error.

There should be an option in PHP to disable bareword string constants and cause a parse error instead IMHO.

Mark