Long floating-point number with extern "C"

#include <stdio.h>
#include <stdlib.h>
extern "C" {void COBRTN
    (double);}

int main()
{
  double x;
  x=3.14159265;
  COBRTN(x);   /* x by value */
  exit(0);
}

IDENTIFICATION DIVISION.
PROGRAM-ID. COBRTN.
ENVIRONMENT DIVISION.
DATA DIVISION.
LINKAGE SECTION.
01 X COMP-2.
PROCEDURE DIVISION USING BY VALUE X.
     DISPLAY X.
     GOBACK.
END PROGRAM COBRTN.