How to convert integer 999999999 to float 999999999.0 instead of 1000000000.0 in C#?

Question

In C#, to convert int to float, we just need to do something like float floatNumber = intNumber or Convert.ToSingle(intNumber). However, when it comes to large number such as 999999999, the system cannot correctly convert the number but convert it into the unwanted number 1E+09. Now the question is, is it possible to convert that large integer into the wanted float number?

Look up "What Every Computer Scientist Should Know About Floating-Point Arithmetic". It's something everyone should read, or at least read enough to know why this happens and to know why testing for floating point equality is a **_really_** bad idea. — Flydog57, Dec 17 '18 at 04:04

score 6 · Accepted Answer · answered Dec 17 '18 at 03:21

6

A 32-bit float can't exactly represent an integer that large: It only has 24 bits with which to do it (one is implicit in the format). In 24 bits you can represent 16777215. 16777216 also fits because it is a power of two. 999999999 can't be represented exactly as a number with at most 24 bits multiplied by a power of 2.

See this answer on SO: https://stackoverflow.com/a/3793950/751579

For more information look up details on IEEE floating point 32-bit and 64-bit formats.

answered Dec 17 '18 at 03:21

davidbak

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This a good explanation, but the practical solution would be to use `decimal'. – tymtam Dec 17 '18 at 22:58
@tymtam - Perhaps. Depends on the OP's use case, which he did not describe. (E.g., maybe double is appropriate.) – davidbak Dec 18 '18 at 00:18

tymtam · Answer 2 · 2018-12-17T22:55:05.973

Can you use decimal type?

Console.WriteLine(999999999.0f.ToString("N"));
Console.WriteLine(999999999.0m.ToString("N"));;

prints

1,000,000,000.00
999,999,999.00

The reference even has a example for a very large number

In this example, the output is formatted by using the currency format string. Notice that x is rounded because the decimal places exceed $0.99. The variable y, which represents the maximum exact digits, is displayed exactly in the correct format.
public class TestDecimalFormat
{
    static void Main()
    {
        decimal x = 0.999m;
        decimal y = 9999999999999999999999999999m;
        Console.WriteLine("My amount = {0:C}", x);
        Console.WriteLine("Your amount = {0:C}", y);
    }
}
/* Output:
    My amount = $1.00
    Your amount = $9,999,999,999,999,999,999,999,999,999.00
*/

How to convert integer 999999999 to float 999999999.0 instead of 1000000000.0 in C#?

2 Answers2