>># include <iostream.h>
>># include <stdlib.h>
Neither of these are legal C++ anymore. They may work on modern compilers and will work on older compilers, but keep in mind that you are working with pre-standard C++.
There is no reason to use global variables when the only function in your program is main.
This has never been correct. main returns an integer.
Here is the same code modernized, corrected, and with consistent formatting.
using namespace std;
double on, lb, gramo, kilo, gina, total;
cout << " \n Put Ur Weight In thE sYsteM EnglIsH ";
cout << "\n ";
cout << "\n libras: ";
cin >> lb;
cout << " onzas: ";
cin >> on;
kilo = lb / 2.2046;
gramo = on / .0352736;
gina = gramo / 1000;
total = kilo + gina;
cout << "\ntu el peso en kilos es " << kilo;
cout << "\nY en gramos es " << gramo;
cout << "\n\n Pero en Total Tu peso es " << total;
cout << " \n\n deseea otra operacion??s/n ";
cin >> no;
cout << "\n";
}while (no != 'n');