Error from compiler on class point slope program

[sierrava06]

I am getting an unresolved external error for the program below. Any ideas on what is causing this error. I still have to write the program to test these functions.

error LNK2019: unresolved external symbol _main referenced in function _mainCRTStartup
fatal error LNK1120: 1 unresolved externals

#include<iostream>
#include<cmath>
using namespace std;

class CartesianPoint
{
	float x,y;
	public:
		CartesianPoint(float x1,float y1)
		{
			x=x1;y=y1;
		}
		void operations()
		{
			cout<<"\n Distance from x-axis : "<<y;
			cout<<"\n Distance from y-axis : "<<x;
			float d;
			d=sqrt(x*x+y*y);
			cout<<"\n Distance from origin : "<<d;
		}
};
class LineSegment
{
	float x1,y1,x2,y2;
	float mx,my;
	public:
		LineSegment(float x11,float y11,float x12,float y12)
		{
			x1=x11;y1=y11;x2=x12;y2=y12;
			CartesianPoint c1(x1,y1),c2(x2,y2);
			c1.operations();
			c2.operations();
		}
		void midpt()
		{
			mx=(x1+x2)/2;
			my=(y1+y2)/2;
			cout<<"\n Line joining ("<<x1<<","<<y1<<") and ("<<x2<<","<<y2<<") :";
			cout<<"\n The mid-point is- ("<<mx<<","<<my<<")";
		}
		void perpbis()
		{
			float m;
			m=(y2-y1)/(x2-x1);
			m=(-1)/m;
			cout<<"\n Equation of perpendicular bisector is: ";
			cout<<"\n y-"<<my<<"="<<m<<"(x-"<<mx<<")";
		}
};
class Line
{
	float m,x,y;
	public:
		Line(float m1,float x1,float y1)
		{
			m=m1;x=x1;y=y1;
		}
		void pseq()
		{
			cout<<"\n Point-Slope Equation is :";
			cout<<"\n y-"<<y<<"="<<m<<"(x-"<<x<<")";
		}
		void intercept()
		{
			
			cout<<" \n Intercept on x-axis: "<<x-y/m;
			cout<<" \n Intercept on y-axis: "<<y-m*x;
		}

};

[Daved]

>> I still have to write the program to test these functions.
That's it. You have to write a main function before you can link everything into an executable. You can make an empty main to get it to finish linking if you want.

[FillYourBrain]

or just don't link. you could select compile rather than build (if its visual studio). If its gcc just use the -c flag