Parameter passing

ACompressed recap

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Value copies in; reference passes the address computed at the call (watch aliasing); value-result copies in and copies back in order on return; name re-evaluates the argument expression at every use (thunks). Trace by keeping a table of the caller’s variables and applying each rule exactly.

BMerged rule card

5.4 Parameter passing: by value, by reference, by value-result, by name; output tracing

• Value: copy in; caller unaffected.
• Reference: pass address (fixed at the call); aliasing possible.
• Value-result: copy in, copy back on return to call-time locations, in order.
• Name: re-evaluate the actual expression at every use (thunk).
• Trace with a table of the caller’s cells.

CInterleaved GATE-style questions

Q1MCQ2 marksTrace

Program P1 of Lesson 5.4 (p(i, a[i]) with i = 0, a = {10, 20, 30}). Under call by value-result the printout is:

• (A) 1 10 20 30
• (B) 2 11 20 30
• (C) 1 11 20 30
• (D) 2 10 21 30

Q2NAT1 markAliasing

For int a = 1; void q(int x, int y) { x = x + 10; y = y * 2; }, what is a after q(a, a) by reference?

Numerical answer: ________

Q3NAT1 markAliasing

Same, by value-result:

Numerical answer: ________

Q4MCQ1 markDefinition

Which mode evaluates the actual parameter every time the formal is used?

• (A) value
• (B) reference
• (C) value-result
• (D) name

Q5MCQ2 marksTrace

With int x = 3; int f(int y) { x = x + 1; return y + x; }, main prints f(x) then x. By reference:

• (A) 7, 4
• (B) 8, 4
• (C) 7, 3
• (D) 8, 3

Q6MSQ2 marksTrace

For the same program, which modes print 7 as the first number?

• (A) value
• (B) reference
• (C) value-result
• (D) name

Q7MCQ1 markLanguages

A Pascal var parameter or a C++ reference parameter is passed:

• (A) by value
• (B) by reference
• (C) by name
• (D) by value-result

Q8NAT2 marksTrace

For P6 (a = 2, f(a, a) with x = x + y; y = x * y; print(x, y)), what is the first printed x under call by value?

Numerical answer: ________