求平方和

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#define NM 50000000
void main()
{
	int i=0,sum=0,t=0;
	clock_t start,finish;
	/*-------------------方法一----------------*/
	start=clock();
	for(i=1;i<=NM;i++)
	{
		sum+=i*i;
	}
	finish=clock();
	printf("sum=%d	used %f seconds\n",sum,(double)(finish-start)/CLOCKS_PER_SEC);
	/*-------------------方法二----------------*/
	/*
		F(x)=x*x
		F(i)=F(i-1)+2i-1;
	*/
	t=0;
	sum=0;
	start=clock();
	for(i=1;i<=NM;i++)
	{
		t+=(i<<1)-1;
		sum+=t;
	}
	finish=clock();
	printf("sum=%d	used %f seconds\n",sum,(double)(finish-start)/CLOCKS_PER_SEC);
}