c语言中如何添加计时函数，统计程序执行的时间

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define M 10000000
#define N 10

short a[M]
;
void assign_array_rows()
{
int i, j;
for (i = 0; i<M; i++)
for (j = 0; j<N; j++)
a[i][j] = 0;
}
void assign_array_cols()
{
int i, j;

for (j = 0; j<N; j++)
for (i = 0; i<M; i++)
a[i][j] = 0;
}

int main()
{
clock_t start, finish;
double  duration;

start = clock();
assign_array_rows();
finish = clock();
duration = (double)(finish - start) / CLOCKS_PER_SEC;
printf("行优先用时： %f seconds\n", duration);

start = clock();
assign_array_cols();
finish = clock();
duration = (double)(finish - start) / CLOCKS_PER_SEC;
printf("列优先用时： %f seconds\n", duration);

system("pause");
return 0;
}