円周率を「米粒を敷き詰めて計算」する方法【C言語】

kome_pi.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>


void now(void)
{
	time_t t = time(NULL);
	struct tm *local = localtime(&t);

	printf("%04d/", local->tm_year + 1900);
	printf("%02d/", local->tm_mon + 1);
	printf("%02d", local->tm_mday);

	printf(" ");

	printf("%02d:", local->tm_hour);
	printf("%02d:", local->tm_min);
	printf("%02d\n", local->tm_sec);
	fflush(stdout);
}

int main(int argc,char *argv[])
{
	unsigned long long  n=8 ;

	if(argc > 1 )
	{
		n=atol( argv[1] ) ;		
	}
    double i,k ,all,en;

	long len = n ;
		for(i=0.0f;i<len;i+=1.0f) n *= 2.0f;

	printf("2^%dまで計算可能,start=%ld \n",sizeof(n)*8,n );
		now();
	while(1)
	{
		double ai = 2.0f / (float)n;
		en = 0.0f ;
		for(i=-1.0f ; i<=1.0f ; i+=ai)
		{
				for(k=-1.0f ; k<=1.0f ; k += ai)
				{

						if( i*i + k*k <= 1.0f) en+=1.0f ;
				}
     	}
		all = (float)n ;
		all *= all ;
		printf("π=%.20f ,{%d},",4.0f* en / all ,len);

		now();
		n *= 2 ;
		len++ ;
	}
	return 0;
}