Question at position 27 Assume we have just started the Postscript interpreter, and the stack is empty. Observe the sequence of operations above. What is the outcome of executing 'x 1 add =' in the postscript REPL?25211611Clear my selection单项选择题
A
25
B
21
C
16
D
11

Question

Question at position 27 Assume we have just started the Postscript interpreter, and the stack is empty. Observe the sequence of operations above. What is the outcome of executing 'x 1 add =' in the postscript REPL?25211611Clear my selection单项选择题

A

25

B

21

C

16

D

11

BlackTom AI · Accepted Answer

To tackle this Postscript question, start by parsing the sequence of operations and what each command does in order.
Option A suggests 25 as the result. This would require the stack to contain 24 + 1, or some combination yielding 25. However, the steps shown do not produce such a sum given the defined values.
Option B proposes 21 as the outcome. This aligns with the logic that the variable x is defined twice and the final value assigned to x is used in the calculation.
Option C proposes 16 as the result. That would imply a different arithmetic result that doesn’t fit with the given values and sequence.
Option D proposes 11 as the result. This would be the case if only 10 and 1 were involved or if the definitions didn’t update as shown.

Now, let’s go through the sequence carefully to track the stack and variable bindings:
- /x 10 def defines a name x bound to 10 in the current dictionary (scope starts at the top-level dictionary).
- 3 dict begin opens a new dictionary context, but def operations still affect the current dictionary as long as they are in scope.
- /x 20 def redefines x to 20 in the active dictionary scope.
- end exits the dictionary context; the binding of x to 20 remains available in the outer scope where x is defined.
- x pushes the value bound to the name x onto the stack. Since x was last defined as 20, 20 is now on the stack.
- 1 pushes the literal 1 onto the stack, so the stack top is 1, just under it is 20.
- add pops the top two values (20 and 1) and pushes their sum, which is 21.
- = outputs the top of the stack, which is 21.

Therefore, Option B (21) correctly reflects the outcome of executing 'x 1 add =' given the described Postscript sequence. The other options correspond to incorrect interpretations of the scoping/ordering:
- 25 would require using 10 and 15 or misapplying the values; it ignores the final redefinition of x to 20.
- 16 would come from adding 15 and 1 or using 10 + 6, neither of which matches the sequence.
- 11 would come from using 10 and 1 without recognizing that x was updated to 20 before the addition.

Question at position 27 Assume we have just started the Postscript interpreter, and the stack is empty. Observe the sequence of operations above. What is the outcome of executing 'x 1 add =' in the postscript REPL?25211611Clear my selection单项选择题

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