Validating an integer value against float in C#

Question

I have a textbox where the user can enter a double point number . For eg:-

etc , the double numbers from the UI can be entered.

In my C# code I have to validate if the user has entered 1 or not.

1.00
1.0000
1.000000

are all considered as 1 and pass the validation . I was thinking of converting to Int

public bool Validate(double number)
{
  int v = Convert.ToInt32(number)
  if(v == 1)
   return true;
}

But the problem is I will lose precision , both 1.00 and 1.001 will result as 1 and incorrectly 1.001 will be returned as true which I dont need. How to check if the user has entered 1.00,1.000,...etc from UI in C#?

Edit : I dont need true for numbers like 1.23, 1.001 etc

Does this answer your question? [Floating point comparison functions for C#](https://stackoverflow.com/questions/3874627/floating-point-comparison-functions-for-c-sharp) — Markus Deibel, Nov 08 '21 at 12:50
I must be missing something - why not just `return (number == 1)`? — Matthew Watson, Nov 08 '21 at 12:58
Note that user can still type something like "1.0000000000000001" and it will be equal to 1 no matter what, because it will parse (with `double.Parse`) as 1 (double doesn't have precision to represent such value). — Evk, Nov 08 '21 at 13:12

score 4 · Answer 1 · answered Nov 08 '21 at 13:08

Comparing the value to 1.0 should do the trick:

bool isOne = val == 1.0;

(Equality comparison of floating-point numbers can be tricky, but this one works the way you'd expect.)

Edit: Using 1 instead of 1.0 also works, as Matthew Watson suggested in the comments.

score 2 · Accepted Answer · answered Nov 08 '21 at 12:51

2

You can use decimal data type

public bool Validate(double number)
{
    var num = decimal.Parse(number.ToString());
    if(num == 1)
        return true;
    return false;
}

answered Nov 08 '21 at 12:51

Maxian Nicu

2,166
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Will it return "true" for `1.23`? =) – Guru Stron Nov 08 '21 at 12:52
No. It will return true only for 1.0, 1.00000, 1.0000000000 or 1 – Maxian Nicu Nov 08 '21 at 12:53
OP needs it to be true for `1.23` – Guru Stron Nov 08 '21 at 12:54
@GuruStron : No. I dont need true for 1.23 – VA1267 Nov 08 '21 at 12:58
1

What's the point to convert double to decimal, though a string, for that? – Evk Nov 08 '21 at 13:01
1

@VA1267 that what your question states - _" eg:- 1.00 1.0000 1.23 1.000000 are all valid."_ I clearly see `1.23` there – Guru Stron Nov 08 '21 at 13:04
@GuruStron : It is valid from UI perspective , they can enter any decimal value . Ok let me edit the question as well to make it clear – VA1267 Nov 08 '21 at 13:09

Validating an integer value against float in C#

2 Answers2