Why we don't need suffix after conversion but during declaration we need it?

Question

Float is not accepting suffix f when converting from string to float using C#. I want to convert string to float & my string already has "F" suffix within it. but the float is not accepting suffix f when converting from string to float & throws an exception.

static void Main()
{
    string any_str = "123.45F";
    float f = float.Parse(any_str);       
    Console.WriteLine(f);
    Console.ReadLine();
}

Have you tried using a lowercase f instead of an uppercase one? — carlos chourio, Jun 09 '19 at 05:37
You could try to replace the f from the string before parsing it to the float value. Using the string.Replace method — carlos chourio, Jun 09 '19 at 05:40
Why do you find that amazing? The 'f'/'F' etc.. are only for code, neither for input nor for output. — TaW, Jun 09 '19 at 05:41
I can do that but I want to know why it will not work after conversion ? — Nitin Rastogi, Jun 09 '19 at 05:43
Why we don´t need suffix after conversion but during declaretion we need it? — Nitin Rastogi, Jun 09 '19 at 05:46
One is for coders&compilers one for normal people! You wouldn't want to show it to your customers, right? So why accept it as input?? — TaW, Jun 09 '19 at 06:31

score 4 · Answer 1 · edited Jun 09 '19 at 07:19

4

Basically float.Parse can't do anything with that f suffix. float.Parse will just take a string representing a numerical value, any extra nonnumerical characters will throw an exception. The f suffix is just for use, by you, in your code itself. So as fahime and Norse said you'll need to get rid of that 'f' before using float.Parse.

edited Jun 09 '19 at 07:19

TaW

53,122
8
69
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answered Jun 09 '19 at 05:55

Sean Woodruff

88
7

Norse · Answer 2 · 2019-06-09T06:00:34.483

I don't think float.Parse has any build in functionality for this, but you could create an extension method for your own convenience.

public static float ToFloat(this string value)
{
    return float.Parse(value.TrimEnd('f', 'F'));
}

Use as such:

any_str.ToFloat();

EDIT: Some may suggest you use Regex to clear out any letters or symbols, but it is not very performant; only use it when you know you will have symbols other than the f or F at the end.

Ali Bahrami · Answer 3 · 2019-06-09T06:18:40.297

Why we don´t need suffix after conversion but during declaration we need it?

By default and by C# specifications every number has a floating point will consider as a Double variable so you need to use an F suffix to create a literal for this type.

// 3.14 is considered a double variable by the compiler so it gives you an error
float myFloat = 3.14;

You might ask why a double variable with value 3.14 cannot be assigned or cast into a float variable?

http://net-informations.com/q/faq/float.html

The Decimal, Double, and Float variable types are different in the way that they store the values. Precision is the main difference where float is a single precision (32 bit) floating point data type, double is a double precision (64 bit) floating point data type and decimal is a 128-bit floating point data type.

Float - 32 bit (7 digits) Double - 64 bit (15-16 digits) The main difference is Floats and Doubles are binary floating point types and a Decimal will store the value as a floating decimal point type. So Decimals have much higher precision and are usually used within monetary (financial) applications that require a high degree of accuracy. But in performance wise Decimals are slower than double and float types.

You can read this answer as well.

And about Parse method:

float.Parse only requires a valid string which means only a string includes [0-9], sign character and the decimal point ( vary by culture for eg [,/.]).

So you only need to get rid of any non-valid chars from your strings then parse it.

You suggested using regex while you downvoted my answer because of the same solution!! — fahime, Jun 09 '19 at 06:17
@fahime I don't give him a solution, He already knows that he can remove the `f` at the end of it, he just wants to know why `f` is required during the declaration and etc ... — Ali Bahrami, Jun 09 '19 at 06:19

score -1 · Answer 4 · answered Jun 09 '19 at 05:42

-1

You need to remove all alphabetical chars in your input:

public static void Main()
{
    string any_str = "123.45F";
    string numberOnly = Regex.Replace(any_str, "[^0-9.]", "");
    float f = float.Parse(numberOnly);       
    Console.WriteLine(f);
    Console.ReadLine();
}

answered Jun 09 '19 at 05:42

fahime

179
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He wants to see if `Parse` could parse it or not. – Ali Bahrami Jun 09 '19 at 05:43
He wants to convert a string to float and faced an exception! So it could be the solution. – fahime Jun 09 '19 at 05:47
2

This code with neither work for valid strings like `-1`, `1.23E+10`, `NaN`, `Infinity` nor for certain locales which use other characters than a period as a separator (e.g. in German it‘s 123,45). Instead of a whitelist approach, a blacklist approach like the one proposed by @Norse is better. – ckuri Jun 09 '19 at 06:03

Why we don't need suffix after conversion but during declaration we need it?

4 Answers4