Unit 1 · Discrete Structures and Optimization

Assuming that the system call fork() never fails, consider the following C programs P1 and P2 executed on a UNIX/Linux system.
P1 P2
int main() {
  fork();
  fork();
  fork();
  printf("Happy\n");
} int main() {
  fork();
  printf("Happy\n");
  fork();
  printf("Happy\n");
  fork();
  printf("Happy\n");
}
Statement I: P1 displays "Happy" 8 times.
Statement II: P2 displays "Happy" 12 times.
In light of the above statements, choose the most appropriate answer.

P1	P2
int main() { fork(); fork(); fork(); printf("Happy\n"); }	int main() { fork(); printf("Happy\n"); fork(); printf("Happy\n"); fork(); printf("Happy\n"); }

Pick an option to check yourself, or open the answer below.

Show answer & explanation

Correct answer: C. Statement I is correct but Statement II is false

Explanation

In P1, three fork() calls run back-to-back with no branching, so the process count doubles at each call: 1→2→4→8; all 8 processes then execute the single printf, so "Happy" is printed 8 times — Statement I is correct. In P2, the printf calls are interleaved between the fork() calls, so the process count reaching each printf is itself doubling: 2 processes execute the first printf, 4 execute the second, and 8 execute the third, giving a total of 2+4+8 = 14 prints, not 12 — Statement II is false. Hence option (iii).

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