Question

2. Run the following C program, and submit the screenshot of the result. Also briefly explain the result.

#include <sys/types.h> #include <stdio.h> #include <unistd.h>

#define SIZE 5

int nums[SIZE] = {0,1,2,3,4};

int main() { int i; pid_t pid; pid = fork();

if (pid == 0) { for (i = 0; i < SIZE; i++) { nums[i] *= -i; printf("CHILD: %d ",nums[i]); /* LINE X */ } } else if (pid > 0) { wait(NULL);

for (i = 0; i < SIZE; i++) printf("PARENT: %d ",nums[i]); /* LINE Y */
}

return 0;
}














3. Run the following program and take a screenshot of the result. Explain the relationship between the created processes. (Hint: if we draw an arrow that points from a process to its child process, what shape can we get?)


#include <sys/types.h> #include <stdio.h> #include <unistd.h>

int main (int argc, char *argv[]) { pid_t childpid = 0; int i, nbrOfProcesses; if (argc != 2) { /* Check for valid number of command-line arguments */ fprintf(stderr, "Usage: %s <processes>\n", argv[0]); return 1; }

/* Convert character string to integer */ nbrOfProcesses = atoi(argv[1]); for (i = 1; i < nbrOfProcesses; i++) { childpid = fork(); if (childpid == -1) { printf("Fork failed"); exit(1); } else if (childpid != 0) // True for a parent break; } // End for

// Each parent prints this line fprintf(stderr, "i: %d process ID: %4ld parent ID: %4ld child ID: %4ld\n", i, (long)getpid(), (long)getppid(), (long)childpid);

sleep(5); // Sleep five seconds

return 0;

} // End main

Answer 1

Code:

#include <sys/types.h>

#include <stdio.h>

#include <unistd.h>

#define SIZE 5

int nums[SIZE] = {0, 1, 2, 3, 4};

int main() {

int i;

pid_t pid;

//fork() is used to create a new child process

pid = fork();

// if(pid == 0) tells if the current process is child process

// LINE X is a part of the child process

if (pid == 0)

{

    for (i = 0; i < SIZE; i++) {

      nums[i] *= -i;

      printf("CHILD: %d ", nums[i]); /* LINE X */

    }

}

// if pid > 0 the the current process is parent process

else if (pid > 0)

{

    // wait(NULL) functions tells parent to wait for child process to complete

    // if wait(NULL) isn't used then the parent process will execute first

    // and LINE Y will be printed first because

    // LINE Y is a part of Parent Process

    wait(NULL);

    for (i = 0; i < SIZE; i++)

      printf("PARENT: %d ", nums[i]); /* LINE Y */

}

return 0;

}

The given program shows the working of Parent and child Process

• pid = fork() is used to create a child process.
• The if (pid == 0) tells the system to execute the true block if child process is running, i.e. LINE X will be executed by the child process.
• The if (pid > 0) tells the system to execute the true block if parent process is running, i.e. LINE Y will be executed by the parent process.
• The function wait(NULL) used in the else if block tells parent process to wait for the child process to complete.
• Usually if wait(NULL) is not used the parent process will be executed first and then the child process will be executed.
• As shown in the Output, LINE X is executed first because wait(NULL) made parent process to wait for child process to complete. After that LINE Y is executed and Parent process is completed.

Output: