GATE CSE 1989 | Question: 8b

Question

Indicate the result of the following program if the language uses (i) static scope rules and (ii) dynamic scope rules.

        var x, y:integer;
        procedure A (var z:integer);
        var x:integer;
        begin x:=1; B; z:= x end;
        procedure B;
        begin x:=x+1 end;
        begin
        x:=5; A(y); write (y)
...end.

Answer 1

Using static rules, we get 1.

Using dynamic rules, we get 2

Comments

Note that these questions are PASCAL-like.
If you see the PASCAL semantics, you shall see that if the formal parameter for a procedure has the keyword $\text{var}$ written before it, then PASCAL considers that the parameter to be call-by-reference.

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Nice

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FOR STATIC SCOPING:

1. Global Variables: x and y are declared globally.
2. Procedure A:
   • Declares a local variable x.
   • Calls procedure B.
   • Updates z with the value of the local x (which is 1).
3. Procedure B:
   • Updates the global x by incrementing it.

Now, when the write(y) statement is executed in the main block:

• x in the main block is 5.
• y in the main block was modified by procedure A, so it's 1.

So, the output under static scope rules would be 1.

FOR DYNAMIC SCOPING:

1. Global Variables: x and y are declared globally.
2. Procedure A:
   • Declares a local variable x.
   • Calls procedure B.
   • Updates z with the value of the local x (which is 1).
3. Procedure B:
   • Updates the global x by incrementing it.

Now, when the write(y) statement is executed in the main block:

• x in the main block is 6 (global x was incremented by procedure B).
• y in the main block was not modified by any procedure, so it's still 0.

So, the output under dynamic scope rules would be 0.

• Static Scope: Output is 1.
• Dynamic Scope: Output is 0