用弦截法求一元三次方程的根

来源：互联网发布：网络教学学费编辑：程序博客网时间：2024/06/11 20:49

网上好多人这样写，经过测试，当第二个数大于6时，程序就出错了，我纠结了一下午，原来是float的问题：把float改为double就好了，第二个代码可以解释为什么.

#include<math.h>#include<stdio.h>float f(double x){return ((x-5)*x+16)*x-80;}float xpoint(float x1,float x2){return (x1*f(x2)-x2*f(x1))/(f(x2)-f(x1));}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;   }elsex2=x;printf("%f\n",fabs(y));}while(fabs(y)>0.000001);    return x;}void main(){  float x,x1,x2,y1,y2;  do  {    printf("INPUT X1,X2:\n");    scanf("%f%f",&x1,&x2);     y1=f(x1);    y2=f(x2);  }while(y1*y2>0);  x=root(x1,x2);  printf("A ROOT IS:%f\n:",x);}

#include<stdio.h>int main(){float i;i=0.0000000000000000000000000000000000001;printf("%f\n",1/3);              printf("%e\n",1/3);

printf("%f\n",1.5/3);             printf("%e\n",1.5/3);printf("%f\n",0.0000001);        //打印0.000000printf("%e\n",i);printf("%f\n",0.00000001);return 0;}