GATE CSE 1998 | Question: 2.13

Question

What is the result of the following program?

    program side-effect (input, output);
    var x, result: integer;
    function f (var x:integer):integer;
    begin
        x:x+1;f:=x;
    end
begin
    x:=5;
    result:=f(x)*f(x);
    writeln(result);
    end

• A. $5$
• B. $25$
• C. $36$
• D. $42$

Comments

The question needs editing. For the correctly edited question, visit: geeksforgeeks (https://www.geeksforgeeks.org/aptitude-gate-cs-1998-question-48/).

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Pascal Syntax. Not C.
var is present before function's parameters. This indicates "Call by Reference"
I would incline towards D) 42

Answer 1

Call by value: $36$,
Call by reference: undefined behaviour for C/C++ but $42$ for languages having $*$ as a sequence point.

$f(x) * f(x);$

If the value of $x$ is being modified inside the function (call by reference) we cannot be sure if this modified value or the old value will be passed as argument for the second call to $f()$. This is because left and right operand of any arithmetic expression in C/C++ can be evaluated in any order. For languages like Java, strict left-right order is maintained.

Comments

 srestha

I tried to run this program in pascal but it is showing fatal error.

how will call by reference work here?

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Rupendra Choudhary    srestha ,how it get 49??? ,1st f(x) will give 6 and second will give 7, so does it be 42?

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@srestha ma’am, 

The function f(x) is returning 6 first. So I think if it is call by reference,then answer will be 42.

Answer 2

Option C.

Since the programming language in the syllabus for GATE is: C. So, I would try to write the closest program for the given construct.

Pass by Value:(which is more likely the case here)

#include<stdio.h>
int x, result;

int f(int x)
{
	x = x+1;
	return x;
}

int main()
{
		x = 5;
		result = f(x)*f(x);
		printf("final result : %d\n",result );

	return 0;
}

Output:

final result : 36

But I would also write the closest program to pass by reference, just for overall analysis.

Pass by reference:

#include <stdio.h>

int x =5;

int f(int *p)
{
	(*p)++;
	

	return *p;
}

int main(int argc, char const *argv[])
{
	int *ptr = &x;

	int out;

	out = f(ptr) * f(ptr);

	printf("output : %d\n",out );
	return 0;
}

Output:

output : 42

 

Comments

thanks for the analysis

Answer 3

Answer is (d) :

Why? Since in question syntax is like pascal we will assume that this segment follows rules of Pascal programming language. Then , there is rule in pascal that if in declaration of formal parameters keyword 'var' is prefixed , then the procedure follows call by reference and modifies the actual values of actual params. So  the answer is 42. 

https://www.tutorialspoint.com/pascal/pascal_call_by_reference.htm

Comments

Whatever you're saying is correct. can't comment about 98 but now GATE don't ask individual language base questions...they will explicitly mention about parameter passing.

Answer 4

int  x ---> global int

//main

x <-5 

result = f(x)*f(x); --------> here out of two f(x) any one can be evaluated first (order of evaluation of function in aritematic operation is undefined in c)

//f(5)

local x = 5+1 = 6

=>f(5) <- 6

//f(5)

local x = 5+1 = 6

=> f(5) <- 6

------------------------------------

result <- 6*6;

 

answer: 36 option C