GATE CS 2015 Set 3 Q.64 (CS Q.54): Functions, Recursion, Scope and Storage Classes

Consider the following C program.

#include <stdio.h>
int f1(void);
int f2(void);
int f3(void);
int x = 10;
int main()
{
    int x = 1;
    x += f1() + f2() + f3() + f2();
    printf("%d", x);
    return 0;
}
int f1() { int x = 25; x++; return x; }
int f2() { static int x = 50; x++; return x; }
int f3() { x *= 10; return x; }

The output of the program is _____.

Your answer

Official answer and solution

Official answer: 230
From: Official GATE 2015 answer key

Solution

Trace variable scopes, lifetime of static variables, and modifications to global state.

The program has:

Global variable int x = 10;
In main(): local int x = 1;
Expression: x += f1() + f2() + f3() + f2();

Trace function calls in sequence:

f1():
- Defines local int x = 25;
- x++; gives 26.
- Returns 26.
f2() (first call):
- Uses static int x = 50; (retains value across calls)
- x++; increments static x to 51.
- Returns 51.
f3():
- Operates on the global variable x (which is 10)
- x *= 10; sets global x = 100.
- Returns 100.
f2() (second call):
- Static x is currently 51.
- x++; increments static x to 52.
- Returns 52.

Sum of return values:

\text{sum} = 26 + 51 + 100 + 52 = 229

In main():
x += 229 sets local x = 1 + 229 = 230.
printf("%d", x); prints 230.

Final answer

230

Common trap

Reinitializing the static variable x in f2() to 50 on the second call instead of retaining its value 51.

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

Source

Paper: GATE 2015 Computer Science and Information Technology (CS) Session 3
Question: 64 of 65, printed as CS Q.54
Section: Computer Science and Information Technology

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