How to create a subtract method in a Math class? - php

Question

I am studying OOP and this is my first study project.
I created a Math class and also created an add method. But when I am trying to create a subtract method I don't know where I am getting a problem.
Please kindly help and give me information where I can get more detailed information on OOP.
<?php
class Math
{
/**
*
* #return int
*/
function add()
{
$args = func_num_args();
$sum = 0;
$i = 0;
for ( $i; $i < $args; $i++ )
{
is_int(func_get_arg($i)) ? $sum += func_get_arg($i) : die('use only integers, please');
}
return $sum;
}
function subtract()
{
$args = func_num_args();
$sub = 0;
$i = 0;
while($i < $args)
{
$sub = func_get_arg($i);
if (is_int(func_get_arg($i)))
{
is_int($sub - func_get_arg($i));
}
}
$i++;
return $sub;
}
}
I am calling this class in my index.php like this:
<?php
include("Math.php");
$c = new Math();
$result = $c->subtract(100,10,20,45);
echo $result;
?>

Answer 1

There are a few small problems here:
Your loop won't ever terminate because the incrementing of $i is outside of your while loop.
The setting of $sub the first time should happen before the while loop. I assume your subtraction function is meant to subtract the latter arguments from the first argument. Right now, $sub is reset every pass through the loop.
$sub's value is never updated by the subtraction operation in your loop. You need to assign a new value to $sub based on the subtraction. You can use the -= shorthand for this just like you used the += shorthand in your add() method.
A working solution would look like this:
$sub = func_get_arg( $i ); // At this point $i == 0
while ( $i < $args ) { // Loop while $i is less than the number of args
$i++; // Increment $i
$operand = func_get_arg( $i ); // Name the argument for clarity
if ( is_int( $operand )) { // Make sure the $operand is an integer
$sub -= $operand; // Update $sub by subtracting $operand from it
} else {
// Do some error handling here...
}
}

Answer 2

I would recommend for you to watch this video The Clean Code Talks -- Inheritance, Polymorphism, & Testing.
This might help you to understand OOP better, and one of examples in the talk is very similar to one you are trying to make.

Answer 3

The functional line is_int($sub - func_get_arg($i)); is incorrect. I think you intend to use this as a ternary operator and add additional logic. Here is my rewrite:
public function subtract() {
$args = func_get_args();
$sub = array_shift($args);
foreach ($args as $arg) {
is_int($sub - $arg) and $sub -= $arg
or die('use only integers please');
}
return $sub;
}

Answer 4

You could also do that using array_reduce() and bcsub() (or other subtraction function):
$sub = array_reduce(array_slice(func_get_args(), 1), 'bcsub', func_get_arg(0));