8-6.cpp

来自「C程序设计（第三版）程序第8章函数源代码 习题答案 谭浩强」· C++ 代码 · 共 41 行

#include  <stdio.h>
#include  <math.h>
    float f(float x)
      {float y;
	y=((x-5.0)*x+16.0)*x-80.0;
	return(y);
}
 float xpoint(float x1,float x2)
	{float y;

	 y=(x1*f(x2)-x2*f(x1))/(f(x2)-f(x1));
	 return(y);
	}
float root(float x1,float x2)
       {float x,y,y1;
	 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);
	 }
       void main()
      {float x1,x2,f1,f2,x;
	do
      {
      printf("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%8.4f\n",x);
	}