I want to detect of my first letter of a string. 

I restrict **.**, **-**, **\_** and **0-9** user can't enter first in a `UITextField`. But suppose an user entry **abc.4c** and set crosser before **.** and delete abc then the string will be **.4c** & when user click submit button that times its not validate. So how can i check first letter is a letter or specific symbol in my string?