LI.5.3 Scoping · GATE 2027 Compiler Design

ACompressed recap

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Static scoping binds a non-local name to the nearest enclosing declaration in the program text; dynamic scoping binds it to the most recently called active procedure that declares it. Trace by deciding, for each procedure, where its non-locals come from (text vs call chain), then simulate, remembering that assignments change that declaration. Nested procedures use access links (follow depth difference) or a display.

BMerged rule card

5.3 Static vs dynamic scoping; tracing program output under each; access links and displays (brief)

Scope: region where a declaration applies; non-local = used but not declared locally.
Static: nearest enclosing declaration in the text (compile time).
Dynamic: most recent active caller that declares it (run time, control links).
Access link → record of the lexically enclosing procedure; hops = depth(user) − depth(declaration).
Display d[i] → most recent record at depth i; save/restore d[i] on call/return.

CInterleaved GATE-style questions

Q1MCQ2 marksTrace

Output under static scoping?

int x = 5;
void A() { x = x + 1; print(x); }
void B() { int x = 10; A(); print(x); }
main() { B(); A(); print(x); }

(A) 6, 10, 7, 7
(B) 11, 11, 6, 6
(C) 6, 10, 6, 6
(D) 11, 10, 7, 7

Q2MCQ2 marksTrace

Same program under dynamic scoping:

(A) 6, 10, 7, 7
(B) 11, 11, 6, 6
(C) 11, 10, 6, 6
(D) 6, 11, 6, 6

Q3NAT2 marksTrace

Under static scoping, what is the first number printed?

int n = 5;
int f(int k) { return k * n; }
int g() { int n = 2; return f(3) + n; }
main() { int n = 10; print(g(), f(1)); }

Numerical answer: ________

Q4NAT2 marksTrace

Same program under dynamic scoping: what is the first number printed?

Numerical answer: ________

Q5MCQ1 markLinks

Access links follow:

(A) the call chain
(B) the lexical nesting of procedures
(C) the heap
(D) the order of declarations

Q6MCQ1 markDisplay

A display entry d[i] points to:

(A) the oldest record at depth i
(B) the most recent active record at nesting depth i
(C) the caller’s record
(D) the global area

Q7NAT1 markHops

A procedure at nesting depth 4 uses a variable declared at depth 2. How many access links are followed?

Numerical answer: ________

Q8MSQ2 marksFacts

Which are true?

(A) Under both rules a local declaration hides an outer one with the same name.
(B) Under dynamic scoping a procedure may change a caller’s local variable through a non-local name.
(C) Static scoping needs the call chain to resolve names.
(D) Most modern languages use static scoping.

Answer Vault

Try the questions first. Open when you are ready to check.

Q1 Answer: (A)2 marks

A always updates the global x: 6 then 7; B prints its own x 10.

(B) is wrong: That is dynamic scoping.
(C) is wrong: The second A makes x 7.
(D) is wrong: A does not see B’s x statically.