nth2

#include<stdio.h>
#include<pthread.h>
#include<time.h>

float *result;//result
int n;//the number which every thread should count

void p(void *i)
{
pthread_mutex_t mutex;//lock
pthread_mutex_init(&mutex, NULL);
pthread_mutex_lock(&mutex);

int a=*((int *)i);
int begin=0;
int end=0;
float x=0,y=0;
begin=a*n+1;
end=(a+1)*n;
int j=0;
float total=0;
for(j=begin;j<=end;j++)
{
if(j%3==0) x=y=1.0;
if(j%3==1) x=y=-1.0;
if(j%3==2) x=y=0.0;
total+=x*y;
}

result[a]=total;

pthread_mutex_unlock(&mutex);//realease the lock
}


int main(int args,char*argv[])
{



int threadnumber;//the number of threadnumber
int length;//

scanf("%d",&threadnumber);
scanf("%d",&length);



pthread_t pt[threadnumber];
int ret;
int i=0;

n=length/threadnumber;//每个线程计算的个数


result=(float*)malloc(sizeof(float)*threadnumber);



int a[threadnumber];
for(i=0;i<threadnumber;i++)
a[i]=i;

for(i=0;i<=threadnumber-2;i++)//开始线程
{
ret=pthread_create(&pt[i],NULL,(void*)p,&a[i]);
if(ret!=0)printf("error\n");
}


int h=0;
float total=0,x=0,y=0;
for(h=(threadnumber-1)*n+1;h<=length;h++)
{
if(h%3==0) x=y=1.0;
if(h%3==1) x=y=-1.0;
if(h%3==2) x=y=0.0;
total+=x*y;

}
pthread_join(pt[0],NULL);
pthread_join(pt[threadnumber-2],NULL);

pthread_mutex_t mutex;
pthread_mutex_init(&mutex, NULL);
pthread_mutex_lock(&mutex);
result[threadnumber-1]=total+1;



float last=0;//count the total
for(i=0;i<threadnumber;i++)
{
last+=result[i];
}
pthread_mutex_unlock(&mutex);

printf("the last result is %f \n ",last);




return (0);
}