GATE CS 2016 Set 1 Q.22 (CS Q.12): Pointers, Arrays and Strings

Consider the following C program.

void f(int, short);
void main()
{
    int i = 100;
    short s = 12;
    short *p = &s;
    __________ ; // call to f()
}

Which one of the following expressions, when placed in the blank above, will NOT result in a type checking error?

f(s, *s)

i = f(i, s)

f(i, *s)

f(i, *p)

Official answer and solution

Official answer: D
From: Official GATE 2016 answer key

Solution

Check C function call types against the function declaration prototype.

The function declaration is:
void f(int, short);
This states that f accepts an int as the first argument, a short as the second argument, and returns void.

The variables in main are declared as:

int i = 100; (type: int)
short s = 12; (type: short)
short *p = &s; (type: short *)

Evaluate each option:

(A) f(s, *s): s is of type short, so dereferencing *s is an invalid indirection error.
(B) i = f(i, s): f returns void, so assigning its result to int i is an illegal assignment error.
(C) f(i, *s): Dereferencing non-pointer *s is an invalid indirection error.
(D) f(i, *p): i is an int, and *p dereferences short * to yield a short. These exactly match the parameter types (int, short), and the void return value is correctly discarded.

Therefore, option D will NOT result in a type checking error.

Final answer

Common trap

Missing that s is a variable of type short rather than a pointer, so *s causes a compile-time indirection error.

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2016 Computer Science and Information Technology (CS) Session 1
Question: 22 of 65, printed as CS Q.12
Section: Computer Science and Information Technology

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