semaphores in mutex replacing while loops
 

Ok two questions in this one.
1. Is it better to use semaphores in a mutex thread program rather than while loops?

I have been looking at some tutorials online and would like a little light shed on the meaning of :
wait(S1);
C--;
if (C < 0) {
signal(S1);
wait(S2);
}
signal(S1);

wait(S1);
C ++;
if (C <= 0)
signal(S2);
else
signal(S1);


I know it has something to do with bool. but do I have to declare S1 or can I declare a different variable for S1 and have it still work?

I figured out how to work with them and what it all means.

But my program is giving me the following error

/tmp/ccejb4CZ.0(.text+0xcd): In function `main`:
: undefinded reference to `thread_function`
collect2: ld returned 1 exit status

in the beginning of my code I defined it as follows

void *thread_function(void *arg)


I use it in the following line

res = pthread_create(&a_thread, NULL, thread_function, NULL);


and again at the end of my code

int main()
{
}

void *thread_function(void *arg)
{
sem_wait(&bin_sem);
while(strncmp("end", work_area, 3) != 0)
{
printf("You input %d characters\n", strlen(work_area) -1);
sem_wait(&bin_sem);
}

Can someone please explain to me this error?