Variables that are declared outside the scope of a function, so that it can be used anywhere in the program is known as Global Variables.

   #include <iostream.h>
   float pi = 3.14;
   int main( )
     {
       int area,rad;
       rad = 100;
       area = pi*rad*rad;
       cout  <<  "Area of a Circle:" << area << '\n';    
       return 0;
     }

In the above example "pi" is declared as global variable outside any function. But the "pi" value is used inside the main function.