Gate 2001
Duration: 1 min
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The screen displays a multiple-choice question from the CS-2001 exam paper asking to identify the false statement among four options provided. The instructor systematically evaluates each option to find the answer. He begins by analyzing option (A), which claims that an unambiguous grammar has the same leftmost and rightmost derivation. He marks this statement as False (F) on the screen. Next, he examines option (B), stating that an LL(1) parser is a top-down parser, and marks this as True (T). He proceeds to option (C), noting that LALR is more powerful than SLR, and marks this as True (T). Finally, he looks at option (D), which asserts that an ambiguous grammar can never be LR(k) for any k, and marks this as True (T). Through this process, he confirms that option (A) is the correct answer.
Chapters
0:00 – 1:05 00:00-01:05
The instructor reads the options aloud from the screen. He focuses on option (A) 'An unambiguous grammar has same leftmost and rightmost derivation' and writes a blue 'F' next to it. He then moves to option (B) 'An LL(1) parser is a top-down parser' and writes a blue 'T' next to it. He continues to option (C) 'LALR is more powerful than SLR' and marks it with a blue 'T'. Finally, he addresses option (D) 'An ambiguous grammar can never be LR(k) for any k' and marks it with a blue 'T'. The instructor concludes that since the question asks for the false statement, option (A) is the answer.
The lesson demonstrates how to approach multiple-choice questions in compiler design by verifying the truth value of each statement. The instructor uses visual markers (T/F) to track his reasoning process, providing a clear method for students to follow. This reinforces the distinction between different types of parsers and the properties of ambiguous versus unambiguous grammars, ensuring students understand the core concepts well.