Echo Warning or Confirmation on Condition [PHP]

Question

What I expect on execution:

The function Email() will be called each time the page loads. If $Valid exists Email() should return either true or false. If $Valid does not exist Email() checks the Postback() (example: has the page been submitted and we're seeing it for the second time?) and if true Validate()s the form fields and either sets $Valid=1 (for true) and sends mail() or sets $Valid=0 (for false).

Now $Valid exists Email() should just return a true or false when called for the second time, say for example by a function to echo a warning or confirmation message if mail() successfully sent or not.

What's happening?

$Valid isn't set it seems when Email() is initially called so when we call Email() a second time the isset($Valid) if clause always returns false.

I really hope you can help, I appreciate any answers and thank you all!

BTW: I know we could "try" and "catch" mail() too but I've cut down the complexity of the code as much as I can so it's easier to digest!

Here's the code I need help with:

function Validate(){
    if(!empty($_POST["From"])&&!empty($_POST["Body"])){
        return true;
    }else{
        return false;
    };
};
function Postback(){
    if(isset($_POST["Return"])){
        return true;
    }else{
        return false;
    };
};
function Email(){
    if(isset($Valid)){
        if($Valid!=0){
            return true;
        }else{
            return false;
        };
    }else{
        if(Postback()){
            if(Validate()){
                $Valid=1;
            }else{
                $Valid=0;
            };
        };
    };
};
Email();

Answer 1

You need to declare $Valid as static if you want its value to be preserved across function calls, for example:

function Email() {
    static $Valid = null;
    if ($Valid !== null) {
        if($Valid!=0){
            return true;
        }else{
            return false;
        };
    } else {
        //etc.
    }
}

See http://php.net/manual/en/language.variables.scope.php:

Note that the value will not be preserved across HTTP requests, if you need that you should look at storing the data in a Session.

Answer 2

You need to somehow preserve $Valid across page loads, e.g. in a session variable.