弦截法求根（循环）OJ

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

// 定义函数f(x)
double f(double x) 
{
    return pow(x, 3) - 5 * pow(x, 2) + 16 * x - 80;
}

// 计算弦与x轴的交点
double xpoint(double x1, double x2) 
{
    double xc= (x1 * f(x2) - x2 * f(x1)) / (f(x2) - f(x1));
    return xc;
}

// 使用弦截法求根
double root(double x1, double x2) 
{
	double xc = xpoint(x1,x2);
	if(fabs(f(xc))<=0.0001) return xc;
    if(f(xc)*f(x1)<0)
    {
    	return root(x1,xc);
	}
	else{
		return root(xc,x2);
	}
}

int main() {
	double x1,x2;
	while(1)
	{
		scanf("%lf %lf", &x1, &x2);
		if(f(x1)*f(x2)<0)
		{
			printf("%.6lf\n",root(x1,x2));
			break;
		}
		else{
			printf("reinput:\n");
		}
	}	
    return 0;
}