How to check if input string value contains x elements on the right and x elements on left

Question

I am trying to make a catch exception for input string for example

if user enters

123test456

the program to say

The first 3 characters must be letter

so it should accept

wowTest456

Answer 1

You can use Take() , with .All() including letter condition,

var validString = inputString
      .Take(3)
      .All(x => Char.IsLetter(x));

---

You can solve it using Regex too. Credit to @JohnathanBarclay.

bool isInvalidString = Regex.IsMatch(inputString, @"^\d{3}");

Explanation:

• ^ : Matches the beginning of the string
• \d : Matches the digit characters
• {3} : Matches 3 tokens.

To make it positive regex just check \w instead of \d

bool validString = Regex.IsMatch(inputString, @"^\w{3}");

Using \w includes _ (underscore) as well, if you don't want _ as a part of first three letters, then you can use range like below

bool validString = Regex.IsMatch(inputString, @"^[a-zA-Z]{3}");

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