Regex Error in Switch Statements

Question

I want to create a program that takes in a string and output just the numbers, hopefully using regex to save effort, here is the following code i have

public void main{
    string str = "abc-123.44def";
    string output = "";
    bool setA = false;

    StringBuilder stb = new StringBuilder();
    for(int i=0; i<str.Length; i++){
        switch(str[i]){
            case 'b':
                setA = foo();
                break;
            case 'c':
                foo2();
                break;
            case '\d':
            case '-':
            case '.':
                if(setA){
                    stb.Append(str[i]);
                }
                break;
            default:
                break;
        }
    }
    output = stb.toString();
}

public void foo(){
    return true;
}

Problem is, the editor gives me a error saying

Unrecognized Escape Sequence

on the '\d' part. Ive seen online sample codes where such usage is allowed so im not sure why my editor is not accepting this. Can someone explain to me what the problem is and how to solve it?

EDIT: It seems like my sample was alittle misleading. I cannot just take out the numbers from the strings by itself since other characters in the string calls different functions and the number characters i want to take out depends on some of them. I updated the code to correct the misinformation.

In `case '\d':`, you need to specify a *char*, not a regex pattern. Check the char with `Char.IsDigit`. — Wiktor Stribiżew, Mar 03 '16 at 09:30
There is no escape character as `\d`. It is a string, not char. Why don't you just write `'d'`? — Soner Gönül, Mar 03 '16 at 09:30
@SonerGönül Because he's not trying to match a `d` character? — Rawling, Mar 03 '16 at 09:33
Do you wanna get `12344` or `abc-.def` as a result? I _might_ be wrong on duplicate.. — Soner Gönül, Mar 03 '16 at 09:36
@Rawling Based on input, that doesn't make sense to use `\d` anywhere in code, honestly. — Soner Gönül, Mar 03 '16 at 09:37

score 1 · Accepted Answer · answered Mar 03 '16 at 12:25

You can use the Char.IsDigit() to check if a char is a digit (as I mentioned in my first comment):

string str = "abc-123.44def";
string output = "";
bool setA = false;

StringBuilder stb = new StringBuilder();
for(int i=0; i<str.Length; i++){
    switch(str[i]){
        case 'b':
          setA = foo();
          break;
        case 'c':
          foo2();
          break;
    //  case '\d': REMOVE IT
        case '-':
        case '.':
          if(setA){
             stb.Append(str[i]);
          }   
          break;
        default:
          if (Char.IsDigit(str[i])) stb.Append(str[i]); // Add this
            break;
          }
    }
    output = stb.ToString();
}

Result:

score 0 · Answer 2 · answered Mar 03 '16 at 09:38

Is this what you are looking for ?

    Regex r = new Regex(@"\d+");
    string s = "abc-123.44def";

    var matches = r.Matches(s);
    List<string> numbersOnly = new List<string>();

    foreach (Match match in matches)
        numbersOnly.Add(match.Value);

    foreach (var number in numbersOnly)
        Console.WriteLine(number);

//output: 
//123
//44

Regex Error in Switch Statements

2 Answers2