Find and extract a number from a string

Question

I have a requirement to find and extract a number contained within a string.

For example, from these strings:

string test = \"1 test\"
string test1 =         


        

Answer 1

go through the string and use Char.IsDigit

string a = "str123";
string b = string.Empty;
int val;

for (int i=0; i< a.Length; i++)
{
    if (Char.IsDigit(a[i]))
        b += a[i];
}

if (b.Length>0)
    val = int.Parse(b);

Answer 2

The question doesn't explicitly state that you just want the characters 0 to 9 but it wouldn't be a stretch to believe that is true from your example set and comments. So here is the code that does that.

        string digitsOnly = String.Empty;
        foreach (char c in s)
        {
            // Do not use IsDigit as it will include more than the characters 0 through to 9
            if (c >= '0' && c <= '9') digitsOnly += c;
        }

Why you don't want to use Char.IsDigit() - Numbers include characters such as fractions, subscripts, superscripts, Roman numerals, currency numerators, encircled numbers, and script-specific digits.

Answer 3

Using @tim-pietzcker answer from above, the following will work for PowerShell.

PS C:\> $str = '1 test'
PS C:\> [regex]::match($str,'\d+').value
1

Answer 4

For those who want decimal number from a string with Regex in TWO line:

decimal result = 0;
decimal.TryParse(Regex.Match(s, @"\d+").Value, out result);

Same thing applys to float, long, etc...

Answer 5

Extension method to get all positive numbers contained in a string:

    public static List<long> Numbers(this string str)
    {
        var nums = new List<long>();
        var start = -1;
        for (int i = 0; i < str.Length; i++)
        {
            if (start < 0 && Char.IsDigit(str[i]))
            {
                start = i;
            }
            else if (start >= 0 && !Char.IsDigit(str[i]))
            {
                nums.Add(long.Parse(str.Substring(start, i - start)));
                start = -1;
            }
        }
        if (start >= 0)
            nums.Add(long.Parse(str.Substring(start, str.Length - start)));
        return nums;
    }

If you want negative numbers as well simply modify this code to handle the minus sign (-)

Given this input:

"I was born in 1989, 27 years ago from now (2016)"

The resulting numbers list will be:

[1989, 27, 2016]

Answer 6

What I use to get Phone Numbers without any punctuation...

var phone = "(787) 763-6511";

string.Join("", phone.ToCharArray().Where(Char.IsDigit));

// result: 7877636511