Verifying that a string contains only letters in C

Question

I have an input string and I want to verify that it contains    Only letters or Only letters and numbers or Only letters  numbers or underscore    To clarify  I have 3 different cases in the code  each calling for different validation  What s the simplest way to achieve this in C

User · Answer

You can loop on the chars of string and check using the Char Method IsLetter but you can also do a trick using String method IndexOfAny to search other charaters that are not suppose to be in the string

User · Answer

Iterate through strings characters and use functions of  Char  called  IsLetter  and  IsDigit    If you need something more specific - use Regex class

User · Answer

If You are a newbie then you can take reference from my code    what i did was to put on a check so that i could only get the Alphabets and white spaces  You can Repeat the for loop after the second if statement to validate the string again          bool check   false          Console WriteLine  Please Enter the Name           name Console ReadLine            for  int i   0  i  lt  name Length  i                        if  name i  gt   a   amp  amp  name i  lt   z     name i                                    check   true                          else                             check   false                 break                                 if  check  false                      Console WriteLine  Enter Valid Value               name   Console ReadLine

User · Answer

Only letters    Regex IsMatch input      a-zA-Z         Only letters and numbers    Regex IsMatch input      a-zA-Z0-9         Only letters  numbers and underscore    Regex IsMatch input      a-zA-Z0-9

User · Answer

bool result   input All Char IsLetter    bool result   input All Char IsLetterOrDigit    bool result   input All c  gt Char IsLetterOrDigit c     c

User · Answer

For those of you who would rather not go with Regex and are on the  NET 2 0 Framework  AKA no LINQ    Only Letters   public static bool IsAllLetters string s        foreach  char c in s                if   Char IsLetter c               return false            return true      Only Numbers       public static bool IsAllDigits string s                foreach  char c in s                        if   Char IsDigit c                   return false                    return true          Only Numbers Or Letters       public static bool IsAllLettersOrDigits string s                foreach  char c in s                        if   Char IsLetterOrDigit c                   return false                    return true          Only Numbers Or Letters Or Underscores       public static bool IsAllLettersOrDigitsOrUnderscores string s                foreach  char c in s                        if   Char IsLetterOrDigit c   amp  amp  c                         return false                    return true

User · Answer

I think is a good case to use Regular Expressions   public bool IsAlpha string input        return Regex IsMatch input     a-zA-Z          public bool IsAlphaNumeric string input        return Regex IsMatch input     a-zA-Z0-9          public bool IsAlphaNumericWithUnderscore string input        return Regex IsMatch input     a-zA-Z0-9

User · Answer

Letters only   Regex IsMatch theString       p L          Letters and numbers   Regex IsMatch theString       p L  p N          Letters  numbers and underscore   Regex IsMatch theString       w         Note  these patterns also match international characters  as opposed to using the a-z construct

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Please find the method to validate if char is letter  number or space  otherwise attach underscore   Be free to modified according your needs   public String CleanStringToLettersNumbers String data        var result   String Empty       foreach  var item in data                var c                 if   int item  gt   97  amp  amp   int item  lt   122                 int item  gt   65  amp  amp   int item  lt   90                 int item  gt   48  amp  amp   int item  lt   57                 int item    32                        c   item                     result   result   c             return result

User · Answer

Recently  I made performance improvements for a function that checks letters in a string with the help of this page    I figured out that the Solutions with regex are 30 times slower than the ones with the Char IsLetterOrDigit check    We were not sure that those Letters or Digits include and we were in need of only Latin characters so implemented our function based on the decompiled version of Char IsLetterOrDigit function   Here is our solution    internal static bool CheckAllowedChars char uc                switch  uc                        case  -               case                  case  A               case  B               case  C               case  D               case  E               case  F               case  G               case  H               case  I               case  J               case  K               case  L               case  M               case  N               case  O               case  P               case  Q               case  R               case  S               case  T               case  U               case  V               case  W               case  X               case  Y               case  Z               case  0               case  1               case  2               case  3               case  4               case  5               case  6               case  7               case  8               case  9                   return true              default                  return false                    And the usage is like this    if  logicalId All c   gt  CheckAllowedChars c          Do your stuff here

[c#] Verifying that a string contains only letters in C#

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