String Parsing: Finite State Machine
Validate an identifier step by step using states, character classes, and explicit transitions.
Rule: the first character must be a letter or underscore.
Current State
Step Explanation
Input Scan
Transition Table
| Current State | Character Class | Next State |
|---|---|---|
| START | LETTER | IN_ID |
| START | UNDERSCORE | IN_ID |
| START | DIGIT | REJECT |
| START | OTHER | REJECT |
| IN_ID | LETTER | IN_ID |
| IN_ID | DIGIT | IN_ID |
| IN_ID | UNDERSCORE | IN_ID |
| IN_ID | OTHER | REJECT |