[SOLVED] Help number format problem..

[chaiwei]

Hi all,

 

I got 2 variable $td and $tc which get the value from the database

 

if(row['side']=='d')
$td+=row['amount'];

else if (row['side']=='c')
$tc+=row['amount'];

echo $td;   // 3600.29
echo $tc;   // 3600.29

if(($td-$tc)<>0){
echo ($td-$tc);   //4.54747350886E-13
}

By right it should not print any value, right?

but where is the 4.54747350886E-13 came from?

 

but if I put

echo number_format($td-$tc);  //0

It shows me 0

 

what is happening behind there?

 

[The Little Guy]

try this:

 

if(($td-$tc) != 0){
echo ($td-$tc);   //4.54747350886E-13
}

[corbin]

4.54747350886E-13

 

Is .000000000000454747350886, which is ridiculously close to 0.

 

What you're coming across is called floating point inaccuracy.

 

 

http://en.wikipedia.org/wiki/IEEE_754

 

It should be mentioned somewhere in there.

 

[The Little Guy]

May want to use the round() function.

 

if(round($td-$tc) != 0){
echo ($td-$tc);   //4.54747350886E-13
}

[corbin]

The common solution is usually to check if x - y < z where z is a float of arbitrary value, and 1 or both of x and y are floats.

 

 

Example:

 

<?php
$x = 5.34;
$y = 5.34;
if($x - $y < .0000001) {
    "x - y is 0!";
}

 

 

Edit: If the larger number is the one being subtracted, the absolute value must be taken.

[chaiwei]

if(($td-$tc) != 0){
echo ($td-$tc);   4.54747350886E-13
}

 

same. also is 4.54747350886E-13

I see,

I try to

echo number_format($tc,50);

it shows me 3,600.28999999999950887286104261875152587890625

which is near to 3600.29

So that's why $td-$tc shows me that 4.54747350886E-13

 

Thanks you guys for helping me out.