GATE CS 2012 Q.49 (CS Q.49): Functions, Recursion, Scope and Storage Classes

Common data questions

Common Data for Questions 48 and 49:

Consider the following C code segment.

int a, b, c = 0;
void prtFun(void);
main() {
    static int a = 1; /* Line 1 */
    prtFun();
    a += 1;
    prtFun();
    printf("\n %d %d ", a, b);
}

void prtFun(void) {
    static int a = 2; /* Line 2 */
    int b = 1;
    a += ++b;
    printf("\n %d %d ", a, b);
}

Shared with question 48.

What output will be generated by the given code segment if:
Line 1 is replaced by auto int a = 1;
Line 2 is replaced by register int a = 2;

3 1
4 1
4 2

4 2
6 1
6 1

4 2
6 2
2 0

4 2
4 2
2 0

Official answer and solution

Official answer: D
From: Official GATE 2012 answer key

Solution

Trace C code execution when static variables are replaced by automatic/register storage variables.

Variable replacements:

In main(): auto int a = 1;
In prtFun(): register int a = 2; (automatic duration; reinitialized on every function entry).

Execution trace:

Call 1 to prtFun():
- Register a initialized to 2, auto b initialized to 1.
- ++b becomes 2.
- a += ++b becomes 2 + 2 = 4.
- Prints 4 2.
In main():
- a += 1 makes main's auto a = 2.
Call 2 to prtFun():
- Because a is a register variable (not static), it is reinitialized to 2!
- Auto b is initialized to 1.
- ++b becomes 2.
- a += ++b becomes 2 + 2 = 4.
- Prints 4 2.
In main():
- Prints main's a (2) and global b (0): 2 0.

Output sequence:
4 2
4 2
2 0
This matches option (D).

Final answer

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

Source

Paper: GATE 2012 Computer Science and Information Technology (CS)
Question: 49 of 65, printed as CS Q.49
Section: Computer Science and Information Technology

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