What are the conditions that are required for the underscores to be used? - FORTRAN

What are the conditions that are required for the underscores to be used?

- FORTRAN uses the CALL statement in which the underscore suffix is being appended and it provides the reference to the non-FORTRAN routines.

- FORTRAN routine is being called so that the mismatch of using the underscore can be avoided manually.

- The criteria of the underscore suffix to avoid the mismatch are as follows:

- If FORTRAN routine calls are written in another language then the FORTRAN language can be have the underscore appended in the definition of the code.
- It can also have the underscore appended in the non-FORTRAN routine.

- If non-FORTRAN routine calls are used to call the FORTRAN routines then the underscore is appended in CALL statement that consists of the FORTRAN routine name.