wait() weird behavior in Ubuntu

Question

I wrote the following program and executed in terminal. But I am confused that the program isn't displaying the results as wait behavior is described on internet. I copied this code from a book.

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
pid_t childid;

if(argc!=2)
{
    printf("Please an argument at terminal\n");
    return 0;
}

int i,n = atoi(argv[1]);

for(i=0;i<n;i++)
{
    childid=fork();
    if(childid==0)
    {
        //sleep(20);
        break;
    }
}
while(wait(NULL)>0);

printf("i= %d\n Process ID %d\n Parent ID %d\n Child ID %d\n",i,getpid(),getppid(),childid);

return 0;

}

Should't the parent process execute the last "printf" statment n time, where n is the number of children created.. What happens when the parent calls while(wait(NULL)>0); and the child is still in excution?

Thanks

Answer 1

The wait() system call suspends execution of the calling process until one of its children terminates.

wait() returns the pid of the child whose state is changed(or say terminated). It returns -1 in error ( when there is no child to wait for ).

So the while loop will be executed 0 times in child (forked) process. And in parent process it will be executed n (no of child process) times.

This program will print the last mesage n+1 times. ( 1 in the main, and n in the children)