Identify if a string is a number

Question

If I have these strings:

1. \"abc\" = false

2. \"123\" = true

3. \"ab2\"

Answer 1

With c# 7 it you can inline the out variable:

if(int.TryParse(str, out int v))
{
}

Answer 2

Hope this helps

string myString = "abc";
double num;
bool isNumber = double.TryParse(myString , out num);

if isNumber 
{
//string is number
}
else
{
//string is not a number
}

Answer 3

You can also use:

stringTest.All(char.IsDigit);

It will return true for all Numeric Digits (not float) and false if input string is any sort of alphanumeric.

Please note: stringTest should not be an empty string as this would pass the test of being numeric.

Answer 4

Try the reges below

new Regex(@"^\d{4}").IsMatch("6")    // false
new Regex(@"^\d{4}").IsMatch("68ab") // false
new Regex(@"^\d{4}").IsMatch("1111abcdefg")
new Regex(@"^\d+").IsMatch("6") // true (any length but at least one digit)

Answer 5

Here is the C# method. Int.TryParse Method (String, Int32)

Answer 6

In case you don't want to use int.Parse or double.Parse, you can roll your own with something like this:

public static class Extensions
{
    public static bool IsNumeric(this string s)
    {
        foreach (char c in s)
        {
            if (!char.IsDigit(c) && c != '.')
            {
                return false;
            }
        }

        return true;
    }
}