Enter the radius of the circle, the area of a circle is determined and output.

#include <stdio.h>    // file contains operations //
Double area (A int)   // define the area function, the area of a circle calculated / /
{
    Double T;    // define the variable //
    T * A * A = 3.14;
    return (T);    // the return value of s // area by calling the back
}      // end function area //
   void main ()    // main function / /
   {
        int R & lt;    // // variables defined
        Double s;    // define variables //
        Scanf ( "% D", & r); / / r value input variable //
        S = area (r); / / function call area, the call // assigns the result S
        the printf ( "area = F% \ n-", s);          // output value of s //
    }      // // end of the function body