setuid in c

#include unistd.h
#include sys/types.h
 int main () {
  int real = getuid();
  int euid = geteuid();
  printf("The REAL UID =: %d\n", real);
  printf("The EFFECTIVE UID =: %d\n", euid);
  printf("setuid%d\n",setuid(euid));
  system("cat /etc/shadow");
}
chmod u+s binary