fortran - Compiling .f file, "undefined reference to 'MAIN_' issue -

i trying compile .f file using g77. tried compile .cmd batch file (as per 1 of ways described in g77 documentation) following content (in .cmd file):

g77 -o gtemp.exe gtemp.f pause 

but when run upper .cmd file, following error message: "undefined reference 'main_'

why happening? gtemp.f file in same folder g77.exe file. thank you.

here code gtemp.f file:

      subroutine gtemp(dif,tmin,tmax,tav,tg)                                    gtemp    2       dimension amon(12),tg(12)                                                 gtemp    3       data amon / 15.,46.,74.,95.,135.,166.,196.,227.,258.,288.,                gtemp    4      1            319.,349. /                                                   gtemp    5       data p,pi,po / 8760.,3.14159265,0.6 /                                     gtemp    6 c                                                                               gtemp    7       beta   = sqrt(pi/(dif*p))*10.                                             gtemp    8       x      = exp(-beta)                                                       gtemp    9       x2     = x*x                                                              gtemp   10       c      = cos(beta)                                                        gtemp   11       s      = sin(beta)                                                        gtemp   12       y      = x2 - 2.*x*c + 1.                                                 gtemp   13       y      = y / (2.*beta*beta)                                               gtemp   14       gm     = sqrt(y)                                                          gtemp   15       z      = (1.-x*(c+s)) / (1.-x*(c-s))                                      gtemp   16       phi    = atan(z)                                                          gtemp   17       bo     = (tmax-tmin)*0.5                                                  gtemp   18       40 i=1,12                                                              gtemp   19       theta  = amon(i)*24.                                                      gtemp   20    40 tg(i)  = tav - bo*cos(2.*(pi/p)*theta-po-phi)*gm + 460.                   gtemp   21       return                                                                    gtemp   22       end                                                                       gtemp   23 

this problem happens when compiler cannot find main program.

create main program follows

program test implicit none   real :: dif, tmin, tmax, tav, tg(12)   call gtemp(dif,tmin,tmax,tav,tg)  contains    subroutine gtemp(dif,tmin,tmax,tav,tg)   .....    end subroutine gtemp  end program test