Question on classes

[jdhilljr]

I am playing with classes but have an odd problem and wondering if anyone can tell me why this is happening. I have 4 classes they all work and give the right answer but only D and M echo the text the others only echo the answer.

<?php
class A
{
    function data_insert($a,$b)
    {
        if (isset($this)) {
            echo get_class($this).' '.$a.' plus '.$b.' = '.$a+$b;
        } else {
            echo "\$this is not defined.\n";
        }
    }
}
class S
{
   function data_insert($a,$b)
    {
        if (isset($this)) {
            echo get_class($this).' '.$a.' minus '.$b.' = '.$a-$b;
        } else {
            echo "\$this is not defined.\n";
        }
    }
}
class M
{
   function data_insert($a,$b)
    {
        if (isset($this)) {
            echo get_class($this).' '.$a.' times '.$b.' = '.$a*$b;
        } else {
            echo "\$this is not defined.\n";
        }
    }
}
class D
{
   function data_insert($a,$b)
    {
        if (isset($this)) {
            echo get_class($this).' '.$a.' divided by '.$b.' = '.$a/$b;
        } else {
            echo "\$this is not defined.\n";
        }
    }
}
$az=0;
while($az<100) {
$ax=rand(1,4);
$class=array(1=>'A',2=>'S',3=>'M',4=>'D');
$d=rand(10,100);
$e=rand(10,100);
$c = new $class[$ax]();
$c->data_insert($d,$e);
echo '<br>';
$az++;
}

?>

If you can't stand behind your troops, stand in front of them.
Semper Fidelis

Jim

 

[feherke]

Hi

That has absolutely nothing to do with classes or with OOP in general.

It is simply matter of Operator Precedence : string concatenation has lower priority than multiplication and division but higher priority than addition and subtraction. So the order of evaluation influence the result :

Interactive shell

[blue]php >[/blue] $a=3; $b=2; var_dump(''.$a+$b,''.$a-$b,''.$a*$b,''.$a/$b);
int(5)
int(1)
string(1) "6"
string(3) "1.5"

Lesson to learn : be kind with the PHP interpreter and do not put it to concatenate things when is not necessary. Simply enumerate the [tt]echo[/tt] parameters separated with comma ( , ) instead of concatenating them :

[b]echo[/b] [COLOR=darkgoldenrod]get_class[/color][teal]([/teal][navy]$this[/navy][teal]),[/teal][green][i]' '[/i][/green][teal],[/teal][navy]$a[/navy][teal],[/teal][green][i]' plus '[/i][/green][teal],[/teal][navy]$b[/navy][teal],[/teal][green][i]' = '[/i][/green][teal],[/teal][navy]$a[/navy][teal]+[/teal][navy]$b[/navy][teal];[/teal]

Feherke.

http://feherke.github.com/

 

[jdhilljr]

Yeah I had just figured that out with the + and - sign

<?php
class Addition
{
    function data_insert($a,$b)
    {
        if (isset($this)) {
		$answer=$a+$b;
            echo get_class($this).' '.$a.' added to '.$b.' = '.$answer;
        } else {
            echo "\$this is not defined.\n";
        }
    }
}
class Multiplication
{
   function data_insert($a,$b)
    {
        if (isset($this)) {
            $answer=$a*$b;
            echo get_class($this).' '.$a.' multiplied by '.$b.' = '.$answer;
        } else {
            echo "\$this is not defined.\n";
        }
    }
}

class Division
{
   function data_insert($a,$b)
    {
        if (isset($this)) {
            $answer=$a/$b;
            echo get_class($this).' '.$a.' divided by '.$b.' = '.$answer;
        } else {
            echo "\$this is not defined.\n";
        }
    }
}
class Subtraction
{
   function data_insert($a,$b)
    {
        if (isset($this)) {
           $answer=$a-$b;
            echo get_class($this).' '.$a.' minus '.$b.' = '.$answer;
        } else {
            echo "\$this is not defined.\n";
        }
    }
}

$az=0;
while($az<100) {
$ax=rand(1,4);
$class=array(1=>'Addition',2=>'Subtraction',3=>'Multiplication',4=>'Division');
$d=rand(10,100);
$e=rand(10,100);
$c = new $class[$ax]();
$c->data_insert($d,$e);
echo '<br>';
$az++;
}

?>

If you can't stand behind your troops, stand in front of them.
Semper Fidelis

Jim