调用参数的次数

I'n just learning PHP by myself, and I have a question, hope you will be able to help.

In fist style

<?php
class Fist_style
{
    function method_1()
    {
        global $a;
        return $a + 1; 
    }

    function method_2()
    {
        global $a;
        return $a - 1;
    }

    function method_3()
    {
        $call_1 = $this->method_1();
        $call_2 = $this->method_2();
    }

    // In this case, how many times $a was called?
}

In second style

<?php
class Second_style
{
    function method_1($a)
    {
        return $a + 1; 
    }

    function method_2($a)
    {
        return $a - 1;
    }

    function method_3()
    {
        global $a;

        //I will call both method_1 and method_2
        $call_1 = $this->method_1($a);
        $call_2 = $this->method_2($a);

        //............
    }

    // In this case, how many times $a was called
}
?>

The questions are inside my code, and what style will better when develop?

Using globals is very often a recipe for disaster - as many people with experience will be happy to tell you.

The normal way of having state in a class is declaring a class property:

<?
class MyClass
{
    public $a;

    function __construct($valueForA) {
        $this->a = $valueForA;
    }

    function increment()
    {
       $this->a += 1; 
    }

    function decrement()
    {
       $this->a -= 1; 
    }

    function plusminus()
    {
        $this->increment();
        $this->decrement();
    }
}

Which can be used like so:

$anInstance = new MyClass(10); // sets a to 10 by calling the __construct method
$anInstance->increment();
echo($anInstance->a); // 11
$anInstance->decrement();
echo($anInstance->a); // 10

Read more about oop in PHP here.

As for the question in your code, the $a is not a method, so it can't be called.

Also, return $a -1; does not change the global $a (not sure if this was the intention).

Edit:

If you have a function increment like

function increment ($var) {
    $var = $var - 1;
    return $var;
}

then the $var is passed in as a value - if you passed in a 5, php only cares about 5, not the name. Example:

$a = 5;
$incremented = increment($a);
echo($a); // echoes 5;
echo($incremented); //echoes 6

I would suggest reading up on scoping in php.