How to convert string to double without rounding error?

Question

Because the following command:

Convert.ToDouble("199998,99")

Results in:

199998.98999999

Already the command:

Convert.ToDouble("199998,98")

Results in:

199998.98000000001

?

Answer 1

Assuming that the culture is right and can use the comma (it seems so), the problem is of numerical rounding of the type double. Unfortunately most programmers do not understand its use and do not know that it cannot be used for numerical accuracy, cannot be used for monetary values.

To solve this use the type decimal. He doesn’t have this problem. He has less performance but the difference is small or null in most situations.

There are several questions about this here with articles linked to give more details. No one should program on monetary or other values that need the exact value without fully understanding all implications.

This goes for any language. It is a characteristic of the processor. The type double, or even float uses the binary form to represent the number and this prevents it from representing all numbers with decimals. There’s nothing you can do. Some programmers think they’ve found the solution. But two most renowned computer scientists have spent a lot of time on this, they’ve tried everything, and there’s no solution but to use some other kind of data that gets the exact representation.

Places to start:

• Question about C#/SQL Server.
• Question about C.
• Question about Mysql.
• Question about culture.