I've a double
variable called x
.
In the code, x
gets assigned a value of 0.1
and I check it in an 'if' statement comparing x
and 0.1
if (x==0.1)
{
----
}
Unfortunately it does not enter the if
statement
Should I use Double
or double
?
What's the reason behind this? Can you suggest a solution for this?
It's a standard problem due to how the computer stores floating point values. Search here for "floating point problem" and you'll find tons of information.
In short – a float/double can't store 0.1
precisely. It will always be a little off.
You can try using the decimal
type which stores numbers in decimal notation. Thus 0.1
will be representable precisely.
You wanted to know the reason:
Float/double are stored as binary fractions, not decimal fractions. To illustrate:
12.34
in decimal notation (what we use) means
1 * 101 + 2 * 100 + 3 * 10-1 + 4 * 10-2
The computer stores floating point numbers in the same way, except it uses base 2
: 10.01
means
1 * 21 + 0 * 20 + 0 * 2-1 + 1 * 2-2
Now, you probably know that there are some numbers that cannot be represented fully with our decimal notation. For example, 1/3
in decimal notation is 0.3333333…
. The same thing happens in binary notation, except that the numbers that cannot be represented precisely are different. Among them is the number 1/10
. In binary notation that is 0.000110011001100…
.
Since the binary notation cannot store it precisely, it is stored in a rounded-off way. Hence your problem.