C#

/// <summary>
///    The method to check whether the string is a numeral.
/// </summary>
public static bool IsNumber(string strNumber)
{
    Regex objNotNumberPattern=new Regex("[^0-9.-]");
    Regex objTwoDotPattern=new Regex("[0-9]*[.][0-9]*[.][0-9]*");
    Regex objTwoMinusPattern=new Regex("[0-9]*[-][0-9]*[-][0-9]*");
    String strValidRealPattern="^([-]|[.]|[-.]|[0-9])[0-9]*[.]*[0-9]+$";
    String strValidIntegerPattern="^([-]|[0-9])[0-9]*$";
    Regex objNumberPattern =new Regex("(" + strValidRealPattern +")|(" + strValidIntegerPattern + ")");
    return !objNotNumberPattern.IsMatch(strNumber) &&
        !objTwoDotPattern.IsMatch(strNumber) &&
        !objTwoMinusPattern.IsMatch(strNumber) &&
        objNumberPattern.IsMatch(strNumber);
}

string s="1234";<br />
bool b = s.Trim("1234567890".ToCharArray()).Equals("");

using System;
using System.Globalization;
 
public class Conversion
{
    private static bool IsNumericTypeCode(TypeCode t) 
    {
        switch (t) 
        {
            case TypeCode.Boolean:
            case TypeCode.Byte:
            case TypeCode.SByte:
            case TypeCode.Int16:
            case TypeCode.UInt16:
            case TypeCode.Int32:
            case TypeCode.UInt32:
            case TypeCode.Int64:
            case TypeCode.UInt64:
            case TypeCode.Single:
            case TypeCode.Double:
            case TypeCode.Decimal:
                return true;
    
            default:
                return false;
        }
    }
    
    public static bool IsNumeric(object expression) 
    {
        string sExp = null;
        IConvertible conv = expression as IConvertible;
        if (null == conv)
        {
            if (null == expression as char[]) 
                return false;
            
            sExp = new string((char[])expression);
        }
        else 
        {
            TypeCode t = conv.GetTypeCode();
            if (IsNumericTypeCode(t)) 
                return true;
            else if (t == TypeCode.String || t == TypeCode.Char) 
                sExp = conv.ToString(null);
        }
        
        if (null == sExp)
            return false;
        else 
            return IsNumeric(sExp);
    }
    
    public static bool IsNumeric(string expression) 
    {
        if (null == expression || 0 == expression.Length) 
            return false;
        else 
        {
            double d;
            return double.TryParse(expression,
                NumberStyles.Any, null, out d);
        }
    }
}

switch (x)
{
    case 1:
           x =4;
           break;
    case 2:
    case 3:
           x = 5;
           break;
    default:
               Console.Write("dog");
}

C:\deepak\test.cs(31): Control cannot fall through from one case label ('default:') to another