Creating String extension function

public static string ToCamelCase(this string str)
{
if (!string.IsNullOrEmpty(str) && str.Length > 1)
{
return Char.ToUpperInvariant(str[0]) + str.Substring(1);
}
return str;
}

Usage:
string text = “test data”;
string camalCaseText = text.ToCamelCase();

Output: Test data

Function declaration should be done outside of main class.

https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/how-to-add-custom-methods-for-linq-queries