C code for calculating Pi.

C.CalculatePi.cpp

#include <iostream>
#include <conio.h>
#include <windows.h>

const int N = 50000;
const int Len = 10 * N / 3;
int J, K, Q, Nines, PreDigit;
LARGE_INTEGER StartTime, EndTime, Frequency;
int PiArray[Len + 1]; // 0 .. Len

int OneLoop(int aIndex)
{
    int x, result;
    aIndex = aIndex * 10 / 3 + 16;
    aIndex = (aIndex > Len) ? Len : aIndex;
    result = 0;

    do {
        x = 10 * PiArray[aIndex] + result * aIndex;
        result = x / (2 * aIndex - 1);
        PiArray[aIndex] = x - result * (2 * aIndex - 1);
        aIndex--;
    } while(aIndex > 0);

    return result;
};

int main()
{
    QueryPerformanceFrequency(&Frequency);
    QueryPerformanceCounter(&StartTime);

    for(J = 1; J <= Len; J++) {
        PiArray[J] = 2;
    }

    PreDigit = 0;
    Nines = 0;

    for(J = 1; J <= N; J++) {
        Q = OneLoop(N - J);
        PiArray[1] = Q % 10;
        Q = Q / 10;

        if(9 == Q) {
            Nines = Nines + 1;
        }
        else {
            if(10 == Q) {
                //std::cout << PreDigit + 1;

                for(K = 1; K <= Nines; K++) {
                    //std::cout << 0;
                }

                PreDigit = 0;
                Nines = 0;
            }
            else {
                //std::cout << PreDigit;
                PreDigit = Q;

                if(Nines != 0) {
                    for(K = 1; K <= Nines; K++) {
                        //std::cout << 9;
                        Nines = 0;
                    }
                }
            }
        }
    }

    //std::cout << PreDigit;
    QueryPerformanceCounter(&EndTime);
    std::cout << std::endl;
    std::cout << "C takes time " << (EndTime.QuadPart - StartTime.QuadPart) * 1.0f / Frequency.QuadPart << std::endl;
    _getch();
}