29_函数的嵌套调用

//_29_函数的嵌套调用
//_29_main.cpp

//使用弦截法求解方程的根

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

//定义函数f，从而实现x^3-8*x^2+12*x-30=0
float f(float);
//定义函数xpoint，求出弦与x轴的焦点横坐标
float xpoint(float,float);
//定义函数root，求解区间(x1,x2)的实根
float root(float,float);

int main()
{
	float x1,x2,f1,f2,x;
	do
	{
		printf("Please input x1,x2:\n");
		scanf("%f,%f",&x1,&x2);
		f1 = f(x1);
		f2 = f(x2);
	}while(f1*f2 > 0);
	x = root(x1,x2);
	printf("A root of equation is %9.6f\n",x);

	system("pause");
	return 0;
}

float f(float x)
{
	float y;
	y = (float)(((x-8.0)*x+12.0)*x-30.0);
	return y;
}
float xpoint(float x1,float x2)
{
	float x;
	x = (x1*f(x2) - x2*f(x1))/(f(x2)-f(x1));
	return x;
}
float root(float x1,float x2)
{
	float x,y;
	float y1 = f(x1);
	do
	{
		x = xpoint(x1,x2);
		y = f(x);
		if(y*y1 > 0)
		{
			y1 = y;
			x1 = x;
		}
		else
		{

			x2 = x;
		}
	}while(fabs(y)>=0.0001);
	return x;
}