Semaphore Example in C

This is a Semaphore example in C. I extended the C Thread example to use semaphores. Every thread created will first try to acquire the semaphore lock and then start printing numbers. After printing is done lock is left so other threads can continue their job. Semaphores is a powerful tool for programmers.
Here is the semaphore example source code in C.

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <pthread.h>
#include <semaphore.h>
#define MAX_THREAD 100

typedef struct {
 int start,end;
} param;
sem_t mysem;
void *count(void *arg){
 sem_wait(&mysem);
 int i =0;
 param *p=(param *)arg;
 printf("\nprintfrom %d  to  %d\n",p->start,p->end);
 for(i =p->start ; i< p->end ; i++){
  printf(" i = %d",i);sleep(1);
 }
 
 sem_post(&mysem);
 return (void*)(1);
}

int main(int argc, char* argv[]) {
 
 if ( sem_init(&mysem,0,1) ) {
  perror("init");
 }
 int n,i;
 pthread_t *threads;
 param *p;

     if (argc != 2) {
      printf ("Usage: %s n\n",argv[0]);
      printf ("\twhere n is no. of threads\n");
      exit(1);
     }

 n=atoi(argv[1]);

    if ((n < 1) || (n > MAX_THREAD)) {
      printf ("arg[1] should be 1 - %d.\n",MAX_THREAD);
      exit(1);
    }

 threads=(pthread_t *)malloc(n*sizeof(*threads));

 p=(param *)malloc(sizeof(param)*n);
 /* Assign args to a struct and start thread */
 for (i=0; i<n; i++) {
  p[i].start=i*100;
  p[i].end=(i+1)*100;
  pthread_create(&threads[i],NULL,count,(void *)(p+i));
 }
 printf("\nWait threads\n");
 sleep(1);
 /* Wait for all threads. */
 int *x = malloc(sizeof(int));
 for (i=0; i<n; i++) {
  pthread_join(threads[i],(void*)x);
 }
 free(p);
 exit(0);
}