Difference between Decimal, Float and Double in .NET

float and double are floating binary point types. In other words, they represent a number like this:

10001.10010110011
The binary number and the location of the binary point are both encoded within the value.

decimal is a floating decimal point type. In other words, they represent a number like this:

12345.65789

Again, the number and the location of the decimal point are both encoded within the value – that's what makes decimal still a floating point type instead of a fixed point type.

The important thing to note is that humans are used to representing non-integers in a decimal form, and expect exact results in decimal representations; not all decimal numbers are exactly representable in binary floating point – 0.1, for example – so if you use a binary floating point value you'll actually get an approximation to 0.1. You'll still get approximations when using a floating decimal point as well – the result of dividing 1 by 3 can't be exactly represented, for example.

As for what to use when:

• For values which are "naturally exact decimals" it's good to use decimal. This is usually suitable for any concepts invented by humans: financial values are the most obvious example, but there are others too. Consider the score given to divers or ice skaters, for example.
• For values which are more artefacts of nature which can't really be measured exactly anyway, float/double are more appropriate. For example, scientific data would usually be represented in this form. Here, the original values won't be "decimally accurate" to start with, so it's not important for the expected results to maintain the "decimal accuracy". Floating binary point types are much faster to work with than decimals.

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How to: Compare decimals in PHP

$a = 0.17;
$b = 1 - 0.83; //0.17
if($a == $b ){
 echo 'a and b are same';
}
else {
 echo 'a and b are not same';
}

In this code it returns the result of the else condition instead of the if condition, even though $a and $b are same.

If you do it like this they should be the same. But note that a characteristic of floating-point values is that calculations which seem to result in the same value do not need to actually be identical. So if $a is a literal .17 and $b arrives there through a calculation it can well be that they are different, albeit both display the same value.

Usually you never compare floating-point values for equality like this, you need to use a smallest acceptable difference:

if (abs(($a-$b)/$b) < 0.00001) {
  echo "same";
}

Something like that.

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Format a number with two decimal places in PHP

To accomplish this you can use number_format()

return number_format((float)$number, 2, '.', '');

Example:

$foo = "105";
echo number_format((float)$foo, 2, '.', '');  // Outputs -> 105.00

This function return a string

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