The following programs measures the time required to access an array 500000 time

Question

The following programs measures the time required to access an array 500000 times using array indexing.

Rewrite the program so that your program accesses the array using pointer notation.

Execute both programs multiple times and compare execution times.

#include

using namespace std;

using namespace std::chrono;

void main()

{

     int i, loop, ary[1000] = {};

     double sum = 0.0;

     __int64 duration;

     high_resolution_clock::time_point t1, t2;

     t1 = high_resolution_clock::now();

     for (i = 0; i < 1000; i++)

          ary[i] = 1;

     for (loop = 0; loop < 500000; loop++)

     {

          for (i = 0; i < 1000; i++)

              sum += ary[i];

     }

     cout << "sum = " << sum << endl;

     t2 = high_resolution_clock::now();

     duration = std::chrono::duration_cast(t2 - t1).count();

     cout << duration << endl << endl;

} // main.

Explanation / Answer

Here is the pointer notation to access the array:

#include<iostream>
using namespace std;
using namespace std::chrono;
void main()
{
int i, loop, ary[1000] = {};
double sum = 0.0;
__int64 duration;
high_resolution_clock::time_point t1, t2;
t1 = high_resolution_clock::now();
for (i = 0; i < 1000; i++)
*(ary + i) = 1;   //Accessing using pointer notation.
for (loop = 0; loop < 500000; loop++)
{
for (i = 0; i < 1000; i++)
sum += *(ary + i);
}
cout << "sum = " << sum << endl;
t2 = high_resolution_clock::now();
duration = std::chrono::duration_cast(t2 - t1).count();
cout << duration << endl << endl;
} // main.

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