数组求和(递归和循环)函数 时间性能测量（最差情形）

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

#define MAX_SIZE 1000

typedef struct 
{
	double duration;
	long repetitions;
}times;

double sum_f(double list[], int n);
double sum_r(double list[], int n);

void timer(double(*sum)(double list[], int n), double list[], int n,
		times *);


int main(void)
{
	double list[MAX_SIZE];
	times F,R;
    printf("function           repetitions   time");
	for(int n=100; n<=MAX_SIZE; n+=100)
	{
		
		for(int i=0; i<n; i++)
		    list[i]=n-i;
//		for(int k=0; k<n; k++)
//		    printf("%f ", list[k]);
//		printf("\n");
		timer(sum_f, list, n, &F);
		timer(sum_r, list, n, &R);

		
		printf("\nF: array_size:%3d  %d   %6.15lf ", n, F.repetitions, F.duration);
		printf("\nR: array_size:%3d  %d   %6.15lf \n", n, R.repetitions, R.duration);
	}
	
    return 0;
}
double sum_f(double list[], int n)
{
	double tempsum=0;
	
	for(int i=0; i<n; i++)
		tempsum+=list[i];
	return tempsum;
}
double sum_r(double list[], int n)
{
	if(n) return sum_r(list, n-1)+list[n-1];
	
	return 0;
}
void timer(double(*sum)(double list[], int n), double list[], int n,
		times *x)
{
	x->repetitions=0;
	clock_t start=clock();
	do{
		x->repetitions++;
		sum(list, n);
	}while(clock()-start<3000);
	
	x->duration=(double)(clock()-start/(3*CLOCKS_PER_SEC));
	x->duration/=x->repetitions;
}