C言語計算プログラムにおけるある関数又はアルゴリズムの実行時間

#include 
#include 
#include 

int main()
{
    long i = 10000000L;
    clock_t start, finish;
    double duration;
    printf( "Time to do %ld empty loops is ", i) ;
    start = clock();
    while( i-- );
    finish = clock();
    duration = (double)(finish - start) / CLOCKS_PER_SEC;
    printf( "%f seconds
", duration );
    return 0;
}