GATE CSE 1996 | Question: 19

Question

Consider the following program in pseudo-Pascal syntax. What is printed by the program if parameter $a$ in procedure $\text{test1}$ is passed as

1. call-by-reference parameter

2. call-by-value-result parameter

program Example (input, output)
var b: integer;
procedure test2:
begin b:=10; end
procedure test1 (a:integer):
begin 	a:=5;
        writeln ('point 1: ', a, b);
        test2;
        writeln ('point 2: ', a, b);
end
begin (*Example*)
b:=3; test1(b);
writeln('point3: ', b);
end

Answer 1

1. Call-by-reference:

• point $1: 5 \; 5 $
• point $2: 10 \;10$
• point $3: 10$

2. Call-by-value-result

• point $1: 5\; 3$
• point $2: 5 \;10$
• point $3: 5$

In call by reference there is no copying of memory location of variable and hence $‘a\text{'}$ in $\text{test1}$ is an alias (same memory location) to global variable $b$. In call-by-value-result, while passing to a function a copy of variable is created and while returning back, the final value is copied back. So, with call-by-value-result, $a$ in $\text{test1}$ is having a separate memory location than $b$. 

Comments

@arjun sir, call by value result point 3 is  5 right ?

as b is passed as argument to test1 with formal parameter a , while returning from the function test1 value of a is copied back to b . which makes b from 10 to 5.

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yes, thats 5. Corrected now :)

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call by value:

point 1: 5 , 3

point 2 : 5,10

point 3: 10