php float problem, 1-1 = 2.22044604925E-16

[bonski]

Good day to all,

Recently I have encountered a problem regarding to float numbers. I have this query that gets the values from database and insert it to an array. These values are decimal (float) numbers. Then basing on these values I have a given value inputted from a textfield, and this given value decrements(subt ract with the values from array) until its last remainder. Here's how it looks like:

//assume that these values are from query to array
$arr = array(0.2, 0.2, 1, 1, 1, 1, 1 ,1);

//now the given from textfield which creates error
$given = (float)2.4;

//this loop gets how many values should be needed
//I dont want to use the whole array values, so I need to check each value that is equal or near to the given value

$check_sum = 0;
$ctr = 0;
for ($a=0; $a<sizeof($arr); $a++) {
 $check_sum = $check_sum + $arr[$a];
 if ($check_sum<$given) {
   $ctr++;
   //if sum is less than the given continue on the loop
 } else if ($check_sum==$given) {
   $ctr++; 
   break;
   // if the sum is equal then stop then loop
 } else {
   $ctr++;
   break;
   //as soon as the sum is already more than the given value then stop
 }

 //now i have figure out the length of my array to be use
 for ($i=0; $i<$ctr; $i++) {
  if ($given>$arr[$i]) {
    
    $answer = $given - $arr[$i];
    echo $given.' - '.$arr[$i].' = '.$answer.'<br />';
    //decrements 
    $given = $given - $arr[$i];
  } else if ($given == $arr[$i]) {
    // if both equal, the loop ends, should display $answer = 0
    echo $given.' - '.$arr[$i].' = '.$answer.'<br />';
  } else {
    //if given is less than the value from array, get the excess value
    $excess = $arr[$i] - $given
    echo $arr[$i].' - '.$given.' = '.$excess.'<br />';
  }
}

//so the output should be
//2.4-0.2 = 2.2
//2.2-0.2 = 2
//2-1 = 1
//1-1 = 0

//but instead, it outputs like this
//2.4-0.2 = 2.2
//2.2-0.2 = 2
//2-1 = 1
//1-1 = 2.22044604925E-16

So now, I know the script is ok.. but why 2.22044604925E-16 instead of zero? I hope someone can give me a clarification so I can revise to this one and prevent the float(2.2204460 4925E-16) to come out, but instead the 0.

Thanks. =)

[bonski]

Hi all, nevermind this.. problem solve, instead of this, i multiple each values with 1000.. coz these values are units in kilograms.. then i converted it into grams.. coz they said 1-1 in float will result to some bug.

thanks