Questions generated by Linux C when using Vfork

#include <stdio.h> #include <sys/types.h> #include <unistd.h>int globvar=5;int main () {   pid_t pid; int var=1, i;  printf ("Fork is diff with  vfork\n ");  // pid=fork ();   pid=vfork ();   switch (PID) {  case  0:    i=3;        while (i-->0) {      printf ("child process is running\n");      Globvar++;     var++;     sleep (1);     }     printf ("Child ' s globvar=%d,var=%d\n", Globvar,var);   break;     default:    i=5;    while (i-->0) {      printf ("parent process is running\n");      globvar++ ;     Var++;     sleep (1);     }    printf ("Parent ' s  globvar=%d,var=%d\n ", Globvar,var);     exit (0);  case -1:     printf ("process creation failed\n");     exit (0);}  return 0;}

The result of the operation is:

Fork is diff with Vfork
Child process is running
Child process is running
Child process is running
Child ' s globvar=8,var=4
Parent process is running
Parent process is running
Parent process is running
Parent process is running
Parent process is running
Parent ' s globvar=13,var=-1216646167

The question comes, why is the Var value not 9????

Questions generated by Linux C when using Vfork