为什么while循环显示2个不同的输出？

Question

Why is while loop showing 2 different outputs?

      $a=1;
    while ($a++ <4) {
       echo $a. "<br>";

    }  // output is 2 3 4 but (4 is not less than 4 )



      $a=1;
    while (++$a <4) {
       echo $a. "<br>";

    }       // output is  2 3

Please, can someone explain me the difference in detail? in $a++ it is showing output 2 3 4 but 4 is not less than 4 in while condition then why it is showing 4 which is not satisfying the condition?

Answer 1

In simple anwer, when ++ use as suffix, php first execute while, then add 1 number to $a, Meaning in first while your start $i is 1.

And when ++ use as prefix, php first add 1 number to $a, then execute while, Meaning last while your start is 2.

This is same your code:

$a=1;
while ($a++ <4) {
   echo $a. "<br>";

}  // output is 2 3 4 but (4 is not less than 4 )
$a++;



$a=1;
$a++;
while (++$a <4) {
   echo $a. "<br>";

}       // output is  2 3