do-while循环仅运行一次

Question

I am trying to make a simple while loop using a class to get the factorial of a number. However, for some reason, the while loop is only returning the value after it has run once.

Here is my code:

<?php
    class Factorial {
      public function calculate($int){
             $intStep = $int-1;
                     do {
                        $int*=$intStep;
                        $int--;
                        return $int;
                       } while($int>0);    
              if (!is_int($int)){
                 echo "entry is not a number";
                 }
              }
            }

$factorial = new Factorial;
echo $factorial->calculate(5);

Answer 1

I see a number of problems with your code:

1. return $int; is run inside the do while loop, which means it'll only ever run once.
2. You're decrementing $int instead of $intStep
3. You're checking if $int is below zero instead of $intStep

Here's your code with all of these problems fixed, it works and returns 15:

class Factorial {

    public function calculate ($int) {
        if (!is_int($int)) {
            echo "entry is not a number";
        }
        $intStep = $int - 1;
        do {
            $int += $intStep;
            $intStep--;
        } while ($intStep > 0);
        return $int;
    }
}

$factorial = new Factorial;
echo $factorial->calculate(5);

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Answer 2

You shouldn't return from your function until your result is ready. Since you return early, you won't finish your calculation.

In general, your life will be easier if you learn how to debug. For PHP, the easiest way would be to echo stuff throughout your code. If you put echo $int inside of your loop it would be more obvious to you what the issue was.

Answer 3

try this

 <?php
            class Factorial {
              public function calculate($num){
          $Factorial = 1;
          $i =1;
                             do{
                              $Factorial *= $i;
                              $i++;
                            }while($i<=$num);
                          return $Factorial;     

                      }
                    }
        $factorial = new Factorial;
        echo $factorial->calculate(5);
?>

Answer 4

Factorial ? Maybe the following code is what you want:

Don't forget negative Numbers.

class Factorial {

    public function calculate ($int) {
        if (!is_int($int)) {
            echo "entry is not a number";
        }
        if ($int == 0 || $int == 1) {
            $result = 1;
        } else if ($int < 0) {
            $result = $this->calculate($int + 1) * $int;
        } else {
            $result = $this->calculate($int - 1) * $int;
        }
        return $result;
    }
}

$factorial = new Factorial;
echo $factorial->calculate(-4);