regex matching alpha character followed by 4 alphanumerics

Question

I need a regex for the following pattern:

• Total of 5 characters (alpha and numeric, nothing else).

• first character must be a letter (A, B, or C only)

• the remaining 4 characters can be number or letter.

Clarifcation: the first letter can only be A, B, or C.

Examples:

• A1234 is valid
• D1234 is invalid

Answer 1

EDIT: Grrr... edited regex due to new "clarification" :)

^[A-C][a-zA-Z0-9]{4}$

EDIT: To explain the above Regex in English...

^ and $ mean "From start to finish" (this ensures that the whole string must perfectly match)

[A-C] means "Match either A, B, or C"

[a-zA-Z0-9]{4} means "Match 4 lower case letters, upper case letters, or numbers"