FORTRAN Program:
You should have your statement start after the 7th column.

      INTEGER  N1, N2
      PRINT *, 'ENTER TWO INTEGERS:'
      READ *, N1,N2
      PRINT *, N1, N2
      CALL SWITCH(N1, N2)
      PRINT *, N1, N2
      STOP
      END

      SUBROUTINE SWITCH(ONE, TWO)
         INTEGER ONE, TWO, TEMP
         TEMP = ONE
         ONE =TWO
         TWO = TEMP
         END

The parameters will be passed into subprogram and copy back to main program.