is it compulsory to have no. 1 to 9 after _
identifier last paragraph
Rules for naming variables in C++ : A variable name should be start with an alphabet or a underscore "_". A variable name can have alphabets "a to z", "A to Z", numbers "0 to 9" and an underscore "_". examples: a a1 _a _1 _a1 a_1 a_11 a13 a16_ _3a abc _abc _ab45 ab45 all of these are correct.
not compulsory at all.. make sure you use identifiers that you remember easily cuz identifiers improves the code readability char fn char ln these aren't the good method of declaring instead use full name char first_name char last_name and avoid special characters.