Why does this function produce so many child processes? - c

Question

I wrote this code in order to calculate the factorial of a number using processes and pipe(). I wanted to pass on the result from the child process to the child process. For example, to create calculate 5! the main which is the father sends the number 1 in the pipe. Then the first child is created and does 1*2, then it pushes in the pipe the number 2, the second child does 2*3 pushes the result in the pipe etc... Also, I use argv[1][0] thinking that we run the program like this (./ex3 5) where 5 is the number of which the factorial we would like to find. After running the program though, I noticed that a lot of child process was created (I only wanted 4). Why is that?
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
int fd[2];
int w,count=2;
void child_creator(){
pid_t child;
child=fork();
if (child==0) {
close(fd[1]);
read(fd[0],&w,sizeof(w));
close(fd[0]);
w=w*count;
count++;
printf("I am child %d , my father is %d , the prod is %d\n",getpid(),getppid(),w);
sleep(1);
close(fd[0]);
write(fd[1],&w,sizeof(w));
close(fd[1]);
}
}
int main(int argc , char **argv){
int fact=argv[1][0]-'0';
pipe(fd);
w=1;
for (int i=0; i<fact-1; i++){
printf("this is i %d\n", i);
child_creator();
}
return 0;
}
After a suggested answer I tried this code:
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
int fd[1000][2];
int w,count=1,j=0;
void child_creator(){
pid_t child;
j++;
pipe(fd[j]);
child=fork();
if (child==0) {
close(fd[j-1][1]);
read(fd[j-1][0],&w,sizeof(w));
close(fd[j-1][0]);
w=w*count;
printf("I am child %d , my father is %d , the prod is %d\n",getpid(),getppid(),w);
sleep(1);
close(fd[j-1][0]);
write(fd[j][1],&w,sizeof(w));
close(fd[j][1]);
exit(0);
}
}
int main(int argc , char **argv){
int fact=argv[1][0]-'0';
w=1;
for (int i=0; i<fact-1; i++){
count++;
child_creator();
sleep(2);
}
return 0;
}

Answer 1

Both the parent and child are returning to the for loop in main(). Since the child doesn't need to do anything after it writes its result, it should just exit rather than returning.
You also have problems with your handling of the pipe file descriptors. You do close(fd[1]) at the beginning of the child, but later try to write(fd[1],&w,sizeof(w)). You can't write to a closed FD. You don't need to close anything until the child is exiting, and exiting a process automatically closes all its files.
void child_creator(){
pid_t child;
child=fork();
if (child==0) {
read(fd[0],&w,sizeof(w));
w=w*count;
count++;
printf("I am child %d , my father is %d , the prod is %d\n",getpid(),getppid(),w);
sleep(1);
write(fd[1],&w,sizeof(w));
exit(0);
}
}