GATE CSE 1988 | Question: 2xv

Question

What is printed by following program, assuming call-by reference method of passing parameters for all variables in the parameter list of procedure P?

program     Main(inout, output);
var     a, b:integer;
        procedure P(x, y, z:integer);
        begin
            y:=y+1
            z:=x+x
        end P;
begin
    a:=2; b:=3;
    p(a+b, a, a);
    Write(a)
end.

Answer 1

let variable "$a$" has address $100$  and "$b$" has $200$ .

and a variable in which "$a+b$" is stored has address $300$.

now $p(300,100,100)$  which represent $x,y,z$

$y:=y+1$  // it makes $a=3$;

$z:=x+x$ //  x means the value contained at address $300$ i.e. $5$

$5+5 =10$  hence value at address $100$ i.e.  variable "$a$" will get the value $10$ .

Hence the value of $a$ i.e. $10$ will be printed.

Comments

if it is pass by reference then why does procedure p mentions integer after z?

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nice explanation @psb

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@psb 

I could not understand your solution. The variable 'a' is stored at location 100 whose value is updated to 3 by the code. Value stored at location 300 is updated to 10 which does not represent variable 'a', rather than it represented 'a+b'. So how 'a' got value 10?

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same problem i coudn't understand properly at last  value of a=3,b=10,c=5

so here write (a) will print 3 clear

where i missed ?

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Value should be 3 or 10 but z write it(a)  last so answer 10.

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y,z  represent address 100.

y = 2 + 1 =3

i.e. y and z both contain 3 now.

Again:

z = x + x

means z = 5 + 5

              z  = 10

So, a is 10 now.