80                                            __ 3.   

        . 
   static (.  3.8.4,   static, 
.81).

  extern   ,   
-  ,      - .  ,
    .    extern
     ,     -  -
    ,      .   -
      .

    .      -
   ,       
.  , ,  ,   .
     ,   ,
     .

     :  -
     .   ,  -
 .        
    .

     .   -
    :

  circle3. 

const double pi = 3.14159; //  
// circle3.

double circle(double radius)
{

return (pi * radius * radius);

}

  cir_main.cpp

#include <iostream.h>
double circle(double);      //  ()

int main()
{

double x;

cout  circle(x)  "    "
 x  endl;

}

  UNIX-    CCcircle3.cpp cir_main.cpp.
 const    pi   ;  
     .    
- ,        extern.