How to validate that input string contains only alphabets, validating that textbox contains only alphabets (letter), so here is some of the ways for doing such task. char have a property named isLetter which is for checking if character is a letter or not, or you can check by the regular expression or you can validate your textbox through regular expression validator in asp.net. Following code demonstrating the various ways of implementation.
Programming Tutorials And Source Code - ASP.NET,C#.NET,MVC,JQuery,JavaScript,SQL Server,Angular,WCF examples