可以===和！=可以互换使用？

Can the relational operator === (used for identical) be used interchangeably with the != operator" and get the same results? Or will I eventually run into issues later down the road when I do larger programs?

I know I will get the same results in the example below, will this always be true?

//example 1  
   <?php
        $a = 1; //integer
        $b = '1'; //string
        if ($a === $b) {     
            echo 'Values and types are same'; 
        }
        else {
            echo 'Values and types are not same';
        }
    ?> 

 // example 2
    <?php
        $a = 1; //integer
        $b = '1'; //string
        if ($a != $b) {     
            echo 'Values and types are not same'; 
        }
        else {
            echo 'Values and types are same';
        }
    ?>

Short answer is, no, you can't interchange them because they check for different things. They are not equivalent operators.

You'll want to use !==

It basically means both values being compared must be of the same type.

When you use ==, the values being compared are typecast if needed.

As you know, === checks the types also.

When you use !=, the values are also typecast, whereas !== checks the values and type, strictly.

You're essentially asking whether !($a != $b) will always be identical to $a === $b. The simple answer is: no. !($a != $b) can be boiled down to $a == $b, which is obviously not the same as $a === $b:

php > var_dump(!('0' != 0));
bool(true)

php > var_dump('0' === 0);
bool(false)

!== is obviously the opposite of ===, so !($a !== $b) will always be identical to $a === $b.