sample.c

#include<pthread.h> 
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int sum;
void *runner(void *param);
int main(int argc, char *argv[]) { 
  pthread_t tid;
  pthread_attr_t attr;
  if (argc != 2){
    fprintf(stderr,"usage: sample <integer value>\n");
    return -1;
  }
  if (atoi(argv[1]) < 0){
    fprintf(stderr,"%d must be >= 0 \n",atoi(argv[1]));
    return -1;
  }
  pthread_attr_init(&attr);
  pthread_create(&tid,&attr,runner,argv[1]);
  pthread_join(tid,NULL);
  printf("sum = %d\n",sum);
} 
void *runner(void *param) { 
  int i, upper = atoi(param);
  sum = 0;
  for (i = 1; i <= upper; i++)
    sum += i; 
  pthread_exit(0); 
}