bisection

#include <bits/stdc++.h>
using namespace std;
float func(float x)
{
    float z;
     z=x*x*x+x*x-1;
    return z;
}
main()
{
    float a,b,sub,fx1,fx2,fxn,x1,x2,xn,E;
    int i;
    E=0.009;
    scanf("%f %f",&x1,&x2);
    fx1=func(x1);
    fx2=func(x2);
    if((fx1>0&&fx2>0)||(fx1<0&&fx2<0))
    {
        printf("no root");
    }
    else
    {
        if(fx1<0)
        {
            a=x1;
            b=x2;
        }
        else
        {
           a=x2;
           b=x1;
        }
        for(i=0;;i++)
        {
        xn=(a+b)/2;
        fxn=func(xn);
        printf("%d app\n x1= %.3f x2=%.3f x4=%.3f x4=%.3f\n",i+1,a,b,xn,fxn);
        if(fxn>0)
        {
            b=xn;
        }
        else
        {
            a=xn;
        }
          sub=abs((b-a)/b);

        if (sub<=E)
        {
            printf("final root=%.3f",a);
            return 0;
        }

        }

    }

}