How to convert char to int?

Question

What is the proper way to convert a char to int? This gives 49:

int val = Convert.ToInt32('1');
//int val = Int32.Parse("1"); // Works

I don't want to convert to string and then parse it.

score 298 · Accepted Answer · answered Sep 08 '10 at 09:03

298

I'm surprised nobody has mentioned the static method built right into System.Char...

int val = (int)Char.GetNumericValue('8');
// val == 8

answered Sep 08 '10 at 09:03

Joel Mueller

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Good spot! +1 Very odd that it returns a `double`, though – Marc Gravell Sep 08 '10 at 09:16
4

I agree, I can't figure out why it returns 'double' - how can a single character possibly represent a floating-point number? – Joel Mueller Sep 08 '10 at 16:25
51

There are many Unicode characters that do represent a non-integer number, e.g., [U+2153](http://www.fileformat.info/info/unicode/char/2153/index.htm). – dtb Sep 13 '10 at 12:24
26

@dtb - I hadn't considered that. `Char.GetNumericValue('⅓')` does indeed return `0.3333...`. Thanks for pointing that out! – Joel Mueller Sep 15 '10 at 17:15
Does inverse function exist? – watbywbarif Apr 21 '15 at 06:57
1

Foot Note: this function is currently not available in NetMF. – GisMofx Aug 10 '15 at 12:32

Marc Gravell · Answer 2 · 2010-09-08T09:13:05.357

40

how about (for char c)

int i = (int)(c - '0');

which does substraction of the char value?

Re the API question (comments), perhaps an extension method?

public static class CharExtensions {
    public static int ParseInt32(this char value) {
        int i = (int)(value - '0');
        if (i < 0 || i > 9) throw new ArgumentOutOfRangeException("value");
        return i;
    }
}

then use int x = c.ParseInt32();

edited Sep 08 '10 at 09:13

answered Sep 08 '10 at 08:16

Marc Gravell

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I should have mentioned, I knew about this but is there any other way? I wanted to know if there is an API to do this? – tvr Sep 08 '10 at 08:22
4

If you want a bahavior similiar to `int.Parse`, i.e. that an exception is thrown on invalid input you would need to add additional bounds checking: `if (i < 0 || i > 9) throw new FormatException();` – Dirk Vollmar Sep 08 '10 at 08:23
@user386338 I'm afraid that there is not. – Eugene Cheverda Sep 08 '10 at 08:25
@user386338 - updated with *an* option re API, also including @0xA3's feedback – Marc Gravell Sep 08 '10 at 09:13
@user386338 - see Joel's answer for an inbuilt API method – Marc Gravell Sep 08 '10 at 09:15
So.. Which should I use? `(int)Char.GetNumericValue(ch);` or `(int)(c - '0');` or `c & 0x0f` (probably faster) ? – Jack Jun 08 '12 at 04:21
@Jack if you are after faster, then time it (using large numbers of iterations) and you'll have your answer – Marc Gravell Jun 08 '12 at 05:50

score 21 · Answer 3 · answered Sep 08 '10 at 08:29

What everyone is forgeting is explaining WHY this happens.

A Char, is basically an integer, but with a pointer in the ASCII table. All characters have a corresponding integer value as you can clearly see when trying to parse it.

Pranay has clearly a different character set, thats why HIS code doesnt work. the only way is

int val = '1' - '0';

because this looks up the integer value in the table of '0' which is then the 'base value' subtracting your number in char format from this will give you the original number.

Grif · Answer 4 · 2010-09-08T09:11:19.030

16

int i = (int)char.GetNumericValue(c);

Yet another option:

int i = c & 0x0f;

This should accomplish this as well.

edited Sep 08 '10 at 09:11

answered Sep 08 '10 at 09:00

Grif

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score 4 · Answer 5 · answered Sep 08 '10 at 08:16

4

int val = '1' - '0';

This can be done using ascii codes where '0' is the lowest and the number characters count up from there

answered Sep 08 '10 at 08:16

Tristan

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This is brilliant! imo the most elegant solution here. – arabisoft Mar 23 '20 at 10:17

score 3 · Answer 6 · answered Sep 08 '10 at 08:17

3

int val = '1' - 48;

answered Sep 08 '10 at 08:17

x2.

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@Luke Xu : '0' has ASCII code 0x30 which is 48 in decimal so this is the same as '1' - '0' – NiKiZe Mar 09 '18 at 13:49

Eugene Cheverda · Answer 7 · 2010-09-08T09:03:04.670

3

You may use the following extension method:

public static class CharExtensions
    {
        public static int CharToInt(this char c)
        {
            if (c < '0' || c > '9')
                throw new ArgumentException("The character should be a number", "c");

            return c - '0';
        }
    }

edited Sep 08 '10 at 09:03

answered Sep 08 '10 at 08:19

Eugene Cheverda

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@0xA3 The range check has to be at the beginning of the method in general. Semantically if we are to convert `char` to `int` we have to check range of the input parameter, not the output `int` value. – Eugene Cheverda Sep 08 '10 at 11:04
There is no need to check result `int` value because the range of numeric chars was performed at the start of the method, so there will be correct resulting value, if specified char is not in the range of numeric chars there will be thrown exception. The same logic as you provided but range check is performed at the beginning of the method. – Eugene Cheverda Sep 08 '10 at 12:09
Sorry, I was misreading your code sample. Sometimes it's hard to see the most obvious things. I'd bet that the code said `if (c < 0 || c > 9)`... – Dirk Vollmar Sep 08 '10 at 13:03

score 1 · Answer 8 · answered Sep 08 '10 at 08:20

1

The most secure way to accomplish this is using Int32.TryParse method. See here: http://dotnetperls.com/int-tryparse

answered Sep 08 '10 at 08:20

MUG4N

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TryParse is for strings not for chars – tvr Sep 08 '10 at 08:40
Yes it is but stille the most secure way to accomplish the conversion – MUG4N Sep 08 '10 at 08:42
1

Converting a single character to an integer is a security matter? – Joel Mueller Sep 08 '10 at 09:06
1

'Secure' in this case means that it won't cause problems if your char isn't actually an ascii number - it could be a multi-byte unicode character. – Robin Bennett May 01 '12 at 10:54

Tomer Wolberg · Answer 9 · 2017-12-26T15:06:59.953

1

int val = '1' & 15;

The binary of the ASCII charecters 0-9 is:

0 - 00110000

1 - 00110001

2 - 00110010

3 - 00110011

4 - 00110100

5 - 00110101

6 - 00110110

7 - 00110111

8 - 00111000

9 - 00111001

and if you take in each one of them the first 4 LSB(using bitwise AND with 8'b00001111 that equels to 15) you get the actual number (0000 = 0,0001=1,0010=2,... )

edited Dec 26 '17 at 15:06

answered Dec 26 '17 at 08:33

Tomer Wolberg

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How does this work in terms of types? you are using a bitwise operator between a char and an int and then returns an int? Does the logical AND uses the binary representation of both the char and the int and return a binary representation and then as you are defining the var as an int it uses that representation? – mitomed Jun 07 '18 at 21:59
@mitnomed yes and if you use byte for example then it uses the byte representation. – Tomer Wolberg Jun 10 '18 at 08:00

score 0 · Answer 10 · edited Oct 29 '19 at 16:51

0

An extension of some other answers that covers hexadecimal representation:

public int CharToInt(char c) 
{
    if (c >= '0' && c <= '9') 
    {
        return c - '0';
    }
    else if (c >= 'a' && c <= 'f') 
    {
        return 10 + c - 'a';
    }
    else if (c >= 'A' && c <= 'F') 
    {
        return 10 + c - 'A';
    }

    return -1;
}

edited Oct 29 '19 at 16:51

Lauren Rutledge

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answered Nov 12 '14 at 01:14

Olek

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score 0 · Answer 11 · answered Jan 23 '15 at 17:04

0

You can try something like this:

int val = Convert.ToInt32("" + '1');

answered Jan 23 '15 at 17:04

briba

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why not just .ToString()? – Veikedo Feb 25 '16 at 09:18
@Veikedo he wants an int, and not a string. – briba Apr 28 '16 at 14:15
6

I mean `Convert.ToInt32('1'.ToString())` – Veikedo Apr 28 '16 at 17:15

How to convert char to int?

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