ISRO CS 2023 Q.10: solution and answer

Official answer: DSource: ISRO's revised and final answer key of 16 February 2024

1. The front end of a compiler works on the source in this order: lexical analysis, then syntax analysis, then semantic analysis. The middle and back end then work on the result.

2. Lexical analysis comes first. It reads the character stream and groups it into tokens. The parser needs tokens as its input, so syntax analysis cannot come before it. Options (a) and (c) begin with syntax analysis, so both are wrong.

3. Syntax analysis comes second. The parser takes the token stream and checks it against the grammar, building a parse tree.

4. Semantic analysis comes third. It works on the parse tree and does type checking and scope checking.

5. Intermediate code generation comes after semantic analysis. It turns the checked tree into an intermediate representation.

6. Code optimization comes after that. The optimizer improves the intermediate code, so it needs that code to exist first. Option (b) puts code optimization before intermediate code generation, so it is wrong.

7. Option (c) also repeats syntax analysis and starts with it, so it is wrong in two ways.

8. Option (d) gives lexical analysis, syntax analysis, semantic analysis, intermediate code generation, code optimization. This is the correct sequence, so the answer is (d).