PHP For Loop with Random Integers

Question

I am fairly new to PHP and I am trying to solve this problem where I need to make a for loop to generate 10 random numbers from the range (1,20) and then output whether they are odd or even.

I am so stuck on this though. So far I have this below, but I know its wrong somewhere. Any help or guidance would be much appreciated.

$rand120 = rand(1, 20); 

for($rand120 = 10; $rand120 <= 20; $rand120++); 
{ 
    echo "$rand120"."<br/>"; 
} 

if ($rand120 % 2 === 0) { 
    echo "$rand120 is even </br>"; 
} else { 
    echo "$rand120 is odd </br>"; 
}

Answer 1

rand() will only return one random number, not a range of numbers. The two parameters is for minimum and maximum value. If you want 20 random values, you need to use that in a loop.

for ($i = 0; $i < 10; $i++) {
    $value = rand(1, 20);
    if ($value % 2 === 0) { 
        echo "$value is even </br>"; 
    } else { 
        echo "$value is odd </br>"; 
    }
}

This, however, will not ensure they are unique. If you want that, you need to add it to an array, and check it each time you generate a new number, like shown below. This will loop the while until there are 10 elements in the array, and only add a new element when it doesn't exist in the array already.

$array = array();
while (count($array) < 10)) {
    $value = rand(1, 20);
    if (!in_array($value, $array) {
        $array[] = $value;
        if ($value % 2 === 0) { 
            echo "$value is even </br>"; 
        } else { 
            echo "$value is odd </br>"; 
        }
    }
}

• Live demo (for-loop)
• Live demo (while-loop)
• PHP.net on rand()

Answer 2

Hey you are on the right track!

Where I think you got a little off base is that you need to create a random number ten times. Whereas you created only one random number.

See my example below with explanations.

<?php

//create a for loop that will do something 10 times in row
for ($i=0;$i<10;$i++) {

    //every time the loop runs, lets create a random number
    //between 1 and 20 using the rand() function
    $currentRandomNumber = rand(1,20);

    //now, if the random number we made on this loop iteration
    //leaves no remainder when divided by two, it must be even,
    //otherwise it must be odd
    if ($currentRandomNumber % 2 === 0) {
        echo $currentRandomNumber . ' is even.';
    } else {
        echo $currentRandomNumber . ' is odd.';
    }
}

?>

Happy learning!

Answer 3

for($i = 0; $i < 10; $i++)
{ 
    $rand120 = rand(1, 20);
    echo "$rand120"."<br/>"; 

    if ($rand120 % 2 === 0) { 
        echo "$rand120 is even </br>"; 
    } else { 
        echo "$rand120 is odd </br>"; 
    }

} 

Explanation

If you want to generate 10 random numbers you should start by looping 10 times. Also rand() returns a single number within the range you give to the function. Therefore, you must call rand every interaction in loop for getting a new random number between 1 and 20.

As you want to tell whether the number is odd or even for every number the if statement ought to go inside the for loop as well.

Answer 4

There is nothing wrong with the other answers on this page. I would like to show you some alternative practices.

Consider this code: (Demo)

for($i=0; $i<10; ++$i){
    echo $rand=rand(1,20),' is ',($rand&1?'odd':'even'),'<br>';
}

Output:

17 is odd
16 is even
17 is odd
4 is even
3 is odd
7 is odd
13 is odd
6 is even
4 is even
18 is even

• The for loop doesn't change much compared to the other answer. Only the position of the ++ incrementation. I always position my ++ before the variable (when it doen't affect the value differently to do so) as standard practice because it has been proven to be faster than "post-incrementing" ($i++) in benchmarks that I have read. This improvement is a micro-optimization that will go unnoticed by your users virtually every time, but I still do it.
• PHP allows you to declare a variable while echoing it. This makes the code more condensed, but also makes it a little uglier (IMO). Just something to show you.
• When concatenating strings in an echo, I always use commas instead of dots. Like my statement about pre-incrementing with ++, using commas is a micro-optimization that performs the same function with a tiny improvement in terms of speed.
• I have written an inline-conditional to determine odd or even. This is used to reduce the total lines necessary to achieve the desired result. Some people do not like inline-conditionals, but they do not bother me as long as they are not too convoluted (e.g. do not contain more nested inline conditionals).

• It is good practice to write DRY code. This means instead of writing everything twice like this:

  if($rand&1){
      echo "$rand is odd<br>";
  }else{
      echo "$rand is even<br>";
  }
  

  You should only write the static components once. My original snippet obeys this technique. The following is another way (but it actually uses more lines of code and more echos):

  echo "$rand is ";
  if($rand&1){
      echo 'odd';
  }else{
      echo 'even';
  }
  echo '<br>';
  

• Lastly, I have implemented the less intuitive bitwise method of determining odd numbers (&1). Demo The advantage here is speed of execution (but again on the scale of your project, it is likely to go unnoticed). I just use this as standard practice.

Opinions on which of these techniques should be used in this case will vary from programmer to programmer, I just wanted to take the opportunity to explain what can be done differently.