UGC NET CSE | December 2018 | Part 2 | Question: 47

Question

Consider the following two $C++$ programs $P1$ and $P2$ and two statements $S1$ and $S2$ about these programs:

$P1$	$P2$
void f(int a, int *b, int &c) { a=1; *b=2; c=3; } int main() { int i=0; f(i, &i, i); count <<i; }	double a=1, b=2; double &f(double &d) { d=4; return b; } int main() { f(a)=5; count < < a< < “:” < < b; }

$S1$ : $P1$ prints out $3.$

$S2$ : $P2$ prints out $4:2$

What can you say about the statements $S1$ and $S2$?

$Code:$

• A. Only $S1$ is true
• B. Only $S2$ is true
• C. Both $S1$ and $S2$ are true
• D. Neither $S1$ nor $S2$ is true

Answer 1

f(i,&i,i); --> f(int a,int *b,int &c);

$'a'$ gets the copy of the variable passed

$'b'$ points to the variable passed to it i.e. to $i$

$\&c$ passing $i$ by reference

a = 1; //updates the value of the copy of i, original i is unaffected
*b = 2; //updates the original i i.e i = 2;
c = 3; //updates the original i i.e. i=3;
..
cout<<i;

This will print $i=3$. So, $S1$ is true

f(a) = 5;

$f(a)$ calls the function $f$

double &f(double &d){
    d=4;
    return b;
}

This function takes a reference variable as a parameter, updates it's value to $4$ i.e. $a=4$ and returns a reference to $double\,b$

f(a)=5; //updates the value of b i.e b = 5

cout<<a<<":"<<b; //prints 4 : 5

So, $S2$ should be false

So, $A$ should be the answer.

Correct me if I'm wrong.

Comments

Upvoted !!!

Nicely explained... And yes official answer is also option A.