Consider a program calling f1(), f2(2), f3() in main. f1() returns 1, f3() returns 5, f2(X) calls f3

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GATE-CS is a competitive examination conducted in India. This question is from the 2023 GATE-CS Compiler Design paper.

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Question

Consider a program calling f1(), f2(2), f3() in main. f1() returns 1, f3() returns 5, f2(X) calls f3() then returns X*f2(X-1) recursively (base case f2(1) returns f1()). Which one of the following options represents the activation tree corresponding to the main function?

Accepted Answer

Correct Answer: (A)Concept -- Activation Tree (from the Dragon Book by Aho et al., Chapter 7):The activation tree shows the call structure of a program. main calls f1(), f2(2), f3() in sequence.f2(2) first calls f3(), then since X=2 != 1, it recursively calls f2(1). f2(1) first calls f3(), then since X=1, returns f1().Activation tree structure:main: children are f1, f2(2), f3 (in order called).f2(2): children are f3 (called first inside f2), f2(1) (recursive call).f2(1): children are f3 (called first), f1 (returned).This matches option (A): main with children f1, f2, f3; f2 having children f3 and f2; the inner f2 having children f3 and f1.

Consider a program calling f1(), f2(2), f3() in main. f1() returns 1, f3() returns 5, f2(X) calls f3() then returns X*f2(X-1) recursively (base case f2(1) returns f1()). Which one of the following options represents the activation tree corresponding to the main function?

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Consider a program calling f1(), f2(2), f3() in main. f1() returns 1, f3() returns 5, f2(X) calls f3() then returns X*f2(X-1) recursively (base case f2(1) returns f1()). Which one of the following options represents the activation tree corresponding to the main function?

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