pipe use during fork - operating-system

Question

When file (pipe) descriptor is shared between parent and child process.
When one of them closes it other one can`t use it any more?
Child after its creation executes close(pipefd[1]);
After that parent can't write any more? because the pipe's write end is closed. but still the below code works. How does it happen?
int main(int argc, char *argv[])
{
int pipefd[2];
pid_t cpid;
char buf;
if (argc != 2)
{
fprintf(stderr, "Usage: %s \n", argv[0]);
exit(EXIT_FAILURE);
}
if (pipe(pipefd) == -1) /* An error has occurred. */
{
fprintf(stderr, "%s", "The call to pipe() has failed.\n");
exit(EXIT_FAILURE);
}
cpid = fork(); /* fork() returns the child process's PID */
if (cpid == -1) /* An error has occurred. */
{
fprintf(stderr, "%s", "The call to fork() has failed.\n");
exit(EXIT_FAILURE);
}
if (cpid == 0)
{ /* Child reads from pipe */
printf("I am the child.\n");
close(pipefd[1]); /* Close unused write end */
printf("The child is about to read from the pipe.\n");
while (read(pipefd[0], &buf, 1) > 0)
write(STDOUT_FILENO, &buf, 1);
write(STDOUT_FILENO, "\n", 1);
close(pipefd[0]);
printf("The child has just echoed from the pipe to standard output.\n");
_exit(EXIT_SUCCESS);
}
else
{ /* Parent writes argv[1] to pipe */
printf("I am the parent.\n");
close(pipefd[0]); /* Close unused read end */
write(pipefd[1], argv[1], strlen(argv[1]));
close(pipefd[1]); /* Closing creates the EOF marker. */
printf("The parent has just written data into the pipe.\n");
printf("The parent will now wait for the child to terminate.\n");
wait(NULL); /* Parent waits for the child to terminate */
exit(EXIT_SUCCESS);
}
return 0;
}