Program that calculates the value of PI

[noodles]

I found this program that calculates the value of pi somewhere on the net:

#include <stdio.h>
#define SCALE 10000
#define MAXARR 2800
#define ARRINIT 2000

main()
{
        int i, j;
        int carry = 0;
        int arr[MAXARR+1];

        for (i = 0; i <= MAXARR; ++i)
                arr[i] = ARRINIT;
        for (i = MAXARR; i; i -= 14) {
                int sum = 0;
                for (j = i; j > 0; --j) {
                        sum = sum*j + SCALE*arr[j];
                        arr[j] = sum % (j*2-1);
                        sum /= (j*2-1);
                }
                printf("%04d", carry + sum/SCALE);
                carry = sum % SCALE;
        }

}

Output:

31415926535897932384626433832795028841971693993751058209749445923078164062862089
98628034825342117067982148086513282306647093844609550582231725359408128481117450
28410270193852110555964462294895493038196442881097566593344612847564823378678316
52712019091456485669234603486104543266482133936072602491412737245870066063155881
74881520920962829254091715364367892590360011330530548820466521384146951941511609
43305727036575959195309218611738193261179310511854807446237996274956735188575272
48912279381830119491298336733624406566430860213949463952247371907021798609437027
70539217176293176752384674818467669405132000568127145263560827785771342757789609
17363717872146844090122495343014654958537105079227968925892354201995611212902196
08640344181598136297747713099605187072113499999983729780499510597317328160963185

Can someone explain what's happening here and why it works?

[Happy_Reaper]

Doesn't the site you picked it up from say anything about it ?

[Yasir_Malik]

I assume that PI can be calculated using a series, so that program must iterate repeatedly using the series formula. Of course, that's not the exact value of PI, but the more iterations you do, the greater the accuracy.

[linuxdude]

if there is nothing wrong with the code then don't post here. This is a math question. You should aks somewhere else.

[twomers]

I'm sure Ken wouldn't mind moving it to the tech board

[noodles]

Doesn't the site you picked it up from say anything about it ?

No, it doesn't. Here's the link: http://www.codecodex.com/wiki/index....pi_calculation

I'm sure Ken wouldn't mind moving it to the tech board

Yeah, please do it.

[jafet]

It appears to use a "spigot" algorithm; try Googling it. BTW there are tons more formulae from en.wikipedia.org/wiki/Pi

[noodles]

It appears to use a "spigot" algorithm; try Googling it. BTW there are tons more formulae from en.wikipedia.org/wiki/Pi

Thanks a lot, Jafet