Formula Error

=I'm not sure why my celsius,temperature and n= pv\rt arent showing up when I compile it. Instead I get this error that the variable f is being used without initial I'm not sure what to do.

#include "stdafx.h"
#include <iostream>
#include <iomanip>

#define PI 3.14159
#define g  9.81
using namespace std;


int main()
{
	
	double Volume,SurfaceArea,Circumference,Area,Sum, Base;
	double Length,Width,Height,SlantHeight,Radius,Value;
	int F,K,C; // temperatures
	double Number, a, l;
	double P,V,R,T

	Base = 10; // This is the base of the triangle
	Height = 3;   
	Area = 1 * Base * Height / 2;
    cout << "\n\t\tThe Area of this beautiful triangle = "
		 << Area;
	
	//Volume of Sphere
	Radius = 6; 
	Height =  3; 
	Volume = 4/3 * PI * Radius * Radius;
	cout << "\n\t\t The volume of this cone = " << Volume;

	//The Sum
	Number = 4;
    a = 1;
	l = 7;

	Sum = Number/2 * (a+l);
	cout<<"\n\n\n The Sum of this sum = " << Sum;


	// Lateral Area of  Cone
	Radius = 3;
	SlantHeight = 4;

	Area = PI * Radius * SlantHeight * 1/2;
    cout<<"\n\n\n The Area of this = " << Area;

//Celcius
    C = 100;
	cout << "\n\t\tThe value of 5 / 9 * (F - 32) = "
		 << 5/9* (F - 32) << " Farenheit";

    //Farenheit
	F = 150;
    cout <<"\n\t\tThe value of 9 / 5 * C + 32 = "
		 << 9/5 * C + 32 <<" Celcius ";

	// I don't know
	P = 3;
	V = 6;
	R = 2;
	T = 7;

	Number = P*V/T*R;

	cout<<"\n\n\t The value of P * V/ T* R = " << Value;
	
	cout << "\n\n\n";
	return 0;
}