ITPEC FE Morning April 2023 Question 5
ITPEC FE Morning April 2023 — Question 5 of 80
BNF Variable Name Matching — identify which string matches a BNF grammar rule.
BNF rules given:
- <variable-name> starts with <letter>, followed by zero or more <letter-and-number>
- <letter> = A | B | C | D | E | F
- <letter-and-number> = <letter> | <number> | _
- <number> = 0–9
Key constraint: the first character must be a <letter> (A–F).
Check each option:
- _B39 — starts with _, not a letter ✗
- 246 — starts with a digit ✗
- 3E5 — starts with a digit ✗
- F5_1 — F (letter) + 5 (number) + _ + 1 (number) ✓
Answer: d) F5_1
Key rule: In BNF grammars, always check what the first production requires — here <variable-name> must begin with <letter>, which eliminates three options immediately.
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