一、基本概念

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>

clock_t start,stop;
double duration;
#define MAXN 10
#define MAXK 1000000

double f1(int n, double a[], double x);
double f2(int n, double a[], double x);
void func();

void func()
{
    duration = ((double)(stop-start))/CLK_TCK/MAXK;
    //CLK_TCK : 表示机器始终每秒所走的时钟打点数
    printf("ticks = %f\n",(double)(stop - start));
    printf("duration = %6.2e\n",duration);
}

double f1(int n, double a[], double x)
{
    int i;
    double p = a[0];
    for( i = 1; i < n; i++ )
    {
        p += ( a[i] * pow( x, i) );
    }
    return p;
}

double f2(int n, double a[], double x)
{
    int i;
    double p = a[n];
    for( i = n; i > 0; i-- )
    {
        p = a[ i - 1 ] + x * p;
    }
    return p;
}

int main()
{
    int i;
    double a[MAXN];
    for ( i = 0; i < MAXN; i++ )
    {
        a[i] = (double)i;
    }
    start = clock();
    for( i = 0; i < MAXK; i++ )
    {
        f1(MAXN-1, a, 1.1);
    }
    stop = clock();
    printf("This is ticks1\n");
    func();

    start = clock();   //捕捉从程序开始运行到clock()被调用时所耗费的时间。这个时间单位是clock tick即“时钟打点”
    for( i = 0; i < MAXK; i++ )
    {
        f2(MAXN-1, a, 1.1);
    }
    stop = clock();
    printf("This is ticks2\n");
    func();

    return 0;
}