C 计算 圆周率（定积分）

// pi.c
// Experiment for PI calculation via Riemann Integral
// By Tangent, [email protected]

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

int main(int argc, char **argv)
{
		// Our formula: PI=4* S(a,b, sqrt(1-x^2), dx
		register double dx = pow(10,-7);
		printf("Experimental dx value is %.7f\n",dx);
		register double S=0.0;
		for(register double x=0.0; x<=1; x+=dx)
		{
				printf("[LAP]\tx=%.7f\t",x);
				register double x_pow = pow(x,2);
				printf("x_pow=%.16f\t",x_pow);
				register double xp_1 = 1-x_pow;
				printf("xp_1=%.20f\t",xp_1);
				register double x_sqrt = sqrt(xp_1);
				printf("x_sqrt=%.40f\t",x_sqrt);
				register double _S = x_sqrt*dx;
				printf("PIECE=%.40f\t",_S);
				S = S+_S;
				printf("S=%.45f\n",S);
		}
		register double pi_res=0.0;
		pi_res = S*4;
		printf("===Results got===\nPI=%.128f\n",pi_res);
		return 0;
}