Generates a 'pi trumpet' with circles coloured by the base 12 digits of Pi, circles shrinking as you go along the series.

pi.c

/* C99 so compile with 'c99 -o pi pi.c'

/* From http://www.codecodex.com/wiki/Calculate_digits_of_pi#C */
#include "stdio.h"
#include "stdlib.h"

//now generates in base 12...
#define SCALE 12 //4096 //8*8*8*8 
#define ARRINIT 2 //1024

void pi_digits(int digits) {
    int carry = 0;
    int digit;
    float radius=250; float X=500, Y=500;
    int arr[digits + 1];
    for (int i = 0; i <= digits; ++i)
        arr[i] = ARRINIT;

    for (int i = digits; i > 0; i-= 14) {
        int sum = 0;
        for (int j = i; j > 0; --j) {
            sum = sum * j + SCALE * arr[j];
            arr[j] = sum % (j * 2 - 1);
            sum /= j * 2 - 1;
        }

printf(" <circle cx=\"%f\" cy=\"%f\" r=\"%f\" fill=\"",X,Y,radius);

// Colours: http://www.rapidtables.com/web/color/Web_Color.htm

        digit=carry + sum / SCALE;
        switch(digit){
        case 0: printf("#FF3333"); break;
        case 1: printf("#FF9933"); break;
        case 2: printf("#FFFF33"); break;
        case 3: printf("#99FF33"); break;
        case 4: printf("#33FF33"); break;
        case 5: printf("#33FF99"); break;
        case 6: printf("#33FFFF"); break;
        case 7: printf("#3399FF"); break;
        case 8: printf("#3333FF"); break;
        case 9: printf("#9933FF"); break;
        case 10: printf("#FF33FF"); break;
        case 11: printf("#FF3399"); break;
        }
printf("\"/>\n");

//printf("%01X", carry + sum / SCALE);

        radius/=1.02;
        X+=radius/20;
        //X+=radius*0.005*(digit-5.5);
        //Y-=radius*0.005*(digit-5.5);
        carry = sum % SCALE;
    }
}

int main(int argc, char** argv) {
    int n = argc == 2 ? atoi(argv[1]) : 10000;

    printf("<svg xmlns=\"http://www.w3.org/2000/svg\" version=\"1.1\">\n");
    pi_digits(n);
    printf("</svg>\n");
    return 0;
}

pi.svg

pi_spiral.c

/* C99 so compile/run with c99 -o pi pi.c -lm && ./pi > pi.svg

/* From http://www.codecodex.com/wiki/Calculate_digits_of_pi#C */
#include "stdio.h"
#include "stdlib.h"
#include "math.h"

//now generates in base 12...
#define SCALE 6 //4096 //8*8*8*8 
#define ARRINIT 2 //1024

//varying base checks against generator:
//http://www.virtuescience.com/pi-in-other-bases.html

void pi_digits(int digits) {
    int carry = 0;
    int digit,colour=1,delta;
    float radius=300; float X=500, Y=500;
    float spiraltheta=0.0, spiralradius=300;
    int arr[digits + 1];
    for (int i = 0; i <= digits; ++i)
        arr[i] = ARRINIT;

    for (int i = digits; i > 0; i-= 14) {
        int sum = 0;
        for (int j = i; j > 0; --j) {
            sum = sum * j + SCALE * arr[j];
            arr[j] = sum % (j * 2 - 1);
            sum /= j * 2 - 1;
        }

X-=400; Y-=400;
spiralradius=hypot(X,Y)/1.02;
spiraltheta=spiraltheta-0.3;
X=spiralradius*cos(spiraltheta);
Y=spiralradius*sin(spiraltheta);
X+=400; Y+=400;

printf(" <circle cx=\"%f\" cy=\"%f\" r=\"%f\" fill=\"",X,Y,radius);

        digit=carry + sum / SCALE;

//colour wheel info:
//http://msdn.microsoft.com/en-us/library/bb263947(v=vs.85).aspx
        //deltas are which direction to jump on 12-member colourwheel
        if (digit==0) delta=6;  //Compl
        if (digit==1) delta=+5; //Split Compl
        if (digit==2) delta=-5; //Split Compl
        if (digit==3) delta=+4; //Triad
        if (digit==4) delta=-4; //Triad
        if (digit==5) delta=1; //similar

        colour=(colour+delta+12)%12;

//        fprintf(stderr,"%d %d %d \t", digit,delta,colour);
        fprintf(stderr,"%d ",digit);

//colours from here: http://www.rapidtables.com/web/color/Web_Color.htm
        switch(colour){
        case 0: printf("#FF3333"); break;
        case 1: printf("#FF9933"); break;
        case 2: printf("#FFFF33"); break;
        case 3: printf("#99FF33"); break;
        case 4: printf("#33FF33"); break;
        case 5: printf("#33FF99"); break;
        case 6: printf("#33FFFF"); break;
        case 7: printf("#3399FF"); break;
        case 8: printf("#3333FF"); break;
        case 9: printf("#9933FF"); break;
        case 10: printf("#FF33FF"); break;
        case 11: printf("#FF3399"); break;
        }
printf("\"/>\n");

//printf("%01X", carry + sum / SCALE);

        radius/=1.03;
        //X+=radius/20;
        //X+=radius*0.005*(digit-5.5);
        //Y-=radius*0.005*(digit-5.5);
        carry = sum % SCALE;
    }
}

int main(int argc, char** argv) {
    int n = argc == 2 ? atoi(argv[1]) : 20000;

    printf("<svg xmlns=\"http://www.w3.org/2000/svg\" version=\"1.1\">\n");
    pi_digits(n);
    printf("</svg>\n");
    return 0;
}