GATE CS 2014 Set 2 Q.52 (CS Q.42): Functions, Recursion, Scope and Storage Classes

Consider the C function given below:

int f(int j)
{
    static int i = 50;
    int k;
    if (i == j)
    {
        printf("something");
        k = f(i);
        return 0;
    }
    else return 0;
}

Which one of the following is TRUE?

The function returns 0 for all values of j.

The function prints the string something for all values of j.

The function returns 0 when j = 50.

The function will exhaust the runtime stack or run into an infinite loop when j = 50.

Official answer and solution

Official answer: D
From: Official GATE 2014 answer key

Solution

Trace the control flow and state of the static variable i when the function is invoked with j = 50.

Static Variable Semantics in C:
- static int i = 50; is initialized once at program startup and retains its value across recursive calls.
- Inside f(int j), i is not modified by any assignment.
Execution with $j = 50$ :
- On initial call f(50):
  - The condition if (i == j) evaluates $50 == 50$ , which is TRUE.
  - The string "something" is printed.
  - The recursive call k = f(i); is issued with argument $i = 50$ .
- On the recursive call f(50):
  - Parameter $j = 50$ .
  - Static variable $i$ remains $50$ .
  - i == j is again TRUE, prints "something", and calls f(50) again.
Resulting Behavior:
- Each recursive call creates a new stack frame on the call stack.
- Because the recursion has no terminating condition when $j = 50$ , it recurses infinitely until memory allocated for the call stack is exhausted, triggering a stack overflow crash.
- Therefore, the function will exhaust the runtime stack or run into an infinite loop when $j = 50$ (Option D).

Final answer

Common trap

Assuming that return 0 is reached; the return statement is placed after the recursive call k = f(i), which never returns.

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

Source

Paper: GATE 2014 Computer Science and Information Technology (CS) Session 2
Question: 52 of 65, printed as CS Q.42
Section: Computer Science and Information Technology

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