Program in C to find root using bisection method?

#include

#include

#include

#define fn(x) (x*x*x-3*x*x-x+9)

void main()

{

clrscr();

float x,a,b,y,y1,y2;

cout<<"enter the initial value a&b"<

cin>>a>>b;

y1=fn(a);

y2=fn(b);

if(y1*y2>0)

{

cout<<"invalid interval"<

}

do

{

x=(a+b)/2;

y=fn(x);

if(y1*y<0)

{

b=x;

y2=y;

}

else

{

a=x;

y1=y;

}

}

while(fabs(b-a)>.001);

cout<<"the root of the equation ="<

getch();

}