Why Convert.ToInt32 or Int32.Parse do not work for me?

Question

It should be a simple code:

        string qty = "211.0000";
        Console.WriteLine(Int32.Parse(qty));

I tried to use Convert.ToInt32 or Int32.Parse, but they all throw an error: Error(s): Exception in user code:

System.FormatException: Input string was not in a correct format.
at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) at Rextester.Program.Main(String[] args)

Did I make any errors to define a string and give a value? I have tried use string or String to define the variable. It works if I use Console.WriteLine(Convert.ToInt32("211.0000")).

BTW I was testing in http://rextester.com/

`"211.0000"` is not a valid *integer* value but a *floating point* one. — Dmitry Bychenko, Apr 04 '17 at 19:15
@Dmitry Bychenko But I was trying to define it as a string first by using double quotes, and then convert it to int. At least Convert.ToInt32 should works isn't it? — James Chen, Apr 04 '17 at 19:17
@Rufus L I am sorry I am confused, shouldn't both of Convert.ToInt32 or Int32.Parse are convert string to number? — James Chen, Apr 04 '17 at 19:18
@JamesChen They do, but only if the string follows the correct *format*. Integers cannot contain decimal points, therefore you cannot parse it as an Int32. — Quietust, Apr 04 '17 at 19:19
@James Only if the string can be converted will they work. Just as you cannot convert "123A000" to an integer, you cannot convert "123.000" to an integer (using those functions) — Rufus L, Apr 04 '17 at 19:20

Dmitry Bychenko · Accepted Answer · 2017-04-04T19:29:50.293

5

When working with floating point values (which have explicit decimal separator .) you should use decimal or double:

  using System.Globalization;

  ...

  string qty = "211.0000";

  // be careful: different cultures have different decimal separators
  decimal result = decimal.Parse(qty, CultureInfo.InvariantCulture);

or

  double result = double.Parse(qty, CultureInfo.InvariantCulture);

having got floating point representation you can round it up to integer

  int value = (int) (result > 0 ? result + 0.5 : result - 0.5);

or

  int value = (int) (Math.Round(result));

edited Apr 04 '17 at 19:29

answered Apr 04 '17 at 19:22

Dmitry Bychenko

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wow didn't know it was that tricky to convert a string of double into integer in C#... – James Chen Apr 04 '17 at 19:27
Why not just call `Math.Round`? – Apr 04 '17 at 19:27
@hvd: sorry, bad habit from pure `C`... – Dmitry Bychenko Apr 04 '17 at 19:30

Rufus L · Answer 2 · 2017-04-04T20:11:27.920

2

I'm changing my answer, hope that's ok, but here's probably the best thing for you is to do a decimal.TryParse, which can handle leading characters like - and ., and then just cast the result to an integer. If the parsing fails, it returns a zero (in the case where the string is not a decimal):

decimal result;
Console.WriteLine(decimal.TryParse(qty, NumberStyles.Any, 
    CultureInfo.InvariantCulture, out result) ? (int)result : 0);

The same code could be used to store the int for later use:

decimal result;
int intResult = decimal.TryParse(qty, NumberStyles.Any,
    CultureInfo.InvariantCulture, out result) ? (int) result : 0;

edited Apr 04 '17 at 20:11

answered Apr 04 '17 at 19:22

Rufus L

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A bit wierd, but counter example: `".123"` expected output `0`, actual - exception – Dmitry Bychenko Apr 04 '17 at 19:28
As I said, you need to have a valid integer in front of the '.' character. – Rufus L Apr 04 '17 at 19:34
1

Updated answer with an example of padding the string with a leading '0' in case it starts with a decimal – Rufus L Apr 04 '17 at 19:36
Now a negative number, e.g. `"-1"` is a counter example... – Dmitry Bychenko Apr 04 '17 at 19:52
Ok, I've changed the answer entirely :) – Rufus L Apr 04 '17 at 19:56
please, add `CultureInfo.InvariantCulture` - "it gives me 2110000, but I want 211" (see comments on Roxy'Pro's answer) – Dmitry Bychenko Apr 04 '17 at 19:58
Ok, I changed it to use InvariantCulture and provided a solution that will also return `0` if the parsing fails (like if you pass it `"hello"`) – Rufus L Apr 04 '17 at 20:06

tRuEsAtM · Answer 3 · 2017-04-04T19:24:26.563

0

You need to use Decimal instead of int

Decimal.Parse(qty);

If you just need the integer part then use the following snippet

Double.Parse(qty, CultureInfo.InvariantCulture);

edited Apr 04 '17 at 19:24

answered Apr 04 '17 at 19:17

tRuEsAtM

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it gives me 2110000, but I want 211... – James Chen Apr 04 '17 at 19:20
Just edited my answer, it will give you the desired results. – tRuEsAtM Apr 04 '17 at 19:20
still 2110000... – James Chen Apr 04 '17 at 19:21
How come `Double.Parse(qty)` gives you 2110000? It gives me 211. – tRuEsAtM Apr 04 '17 at 19:22
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@JamesChen By any chance is your program running with a locale which interprets "." as a thousands separator and "," as a fraction separator (e.g. one of numerous European locales)? – Quietust Apr 04 '17 at 19:23
'string qty = "211.0000"; Console.WriteLine(Double.Parse(qty));' Right? I really get 2110000, and i am pretty sure i was using dot... – James Chen Apr 04 '17 at 19:25
@JamesChen Try the edited version with `CultureInfo.InvariantCulture` – tRuEsAtM Apr 04 '17 at 19:26
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sorry i saw Dmitry Bychenko comes up first of that solution, so i will select him :-) – James Chen Apr 04 '17 at 19:30

Roxy'Pro · Answer 4 · 2017-04-04T19:22:49.587

0

The value you provided is not an integer, before everything what you might try is converting it to a decimal and after that use Convert.ToInt32 from mscorlib because Integers cannot contain decimal points, soo that means you cannot parse it as an Int32, please follow next example:

string value = String.Format("{0:0.00}", 123.4567);      // "123.46"
decimal d = decimal.Parse(value);
Convert.ToInt32(d);

edited Apr 04 '17 at 19:22

answered Apr 04 '17 at 19:19

Roxy'Pro

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it gives me 2110000, but I want 211 – James Chen Apr 04 '17 at 19:20
@JamesChen check for edit – Roxy'Pro Apr 04 '17 at 19:22
@JamesChen If you do not specify culture info (`IFormatProvider`), the current one will be used. On `rextester.com` that will be _German (Germany)_. Therefore a comma is required if you want a decimal separator. So `decimal.Parse("211,0000")` will give `211` with that culture, while `decimal.Parse("211.0000")` gives `2110000`. – Jeppe Stig Nielsen Apr 04 '17 at 20:12

Why Convert.ToInt32 or Int32.Parse do not work for me?

4 Answers4