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Here's the same program coded in modern Fortran 90: (Note Fortran 90 can be written in free form and need not start in column 7). Subroutines and functions may call themselves only if they are explicitly declared with the recursive keyword. For N = 5, the following output is produced: x = 1 x = 2 x = 3 x = 4 x = 5ДЇortran 90 (and 95), on the other hand, supports recursion directly.

This routine simply asks the user how many times to make SUB1 call itself, and then each time SUB1 is executed it increments X and prints the value after each increment. In fact, on every system I've tried so far, this routine works perfectly. N) THEN X = X + 1 PRINT *, 'x = ', X CALL DUMSUB(X,DUMSUB) END IF ENDI've read in some texts that indirect reference is not allowed, but ask yourself 'How can SUB1 possibly know that it's actually calling itself when it calls the dummy subroutine?' It can't, and thus this must work. PROGRAM MAIN INTEGER N, X EXTERNAL SUB1 COMMON /GLOBALS/ N X = 0 PRINT *, 'Enter number of repeats' READ (*,*) N CALL SUB1(X,SUB1) END SUBROUTINE SUB1(X,DUMSUB) INTEGER N, X EXTERNAL DUMSUB COMMON /GLOBALS/ N IF(X. The subroutine can then call itself by calling the dummy subroutine. However, one can implement recursion in a round about way by passing the subroutine as an argument to itself. Attempting to do such will result in a compile time error with compilers that adhere to the FORTRAN 77 standard. FORTRAN 77 subroutines and functions are not allowed to call themselves directly.

SIMPLY FORTRAN COMPILER HOW TO

Example 1: How to write recursive routines in FORTRAN 77Д®xample 2: Behavior of local variables in recursive routines in FORTRAN 77Д®xample 3: Use of the DATA statement in recursive routines in FORTRAN 77Д®xample 4: Summary of local variable behavior on several platforms.Д®xample 1: Recursive Routines in FORTRAN 77 (and Fortran 90)First let me say that I think every serious Fortran programmer should always write new code in Fortran 90 or Fortran 95, but for those of you stuck on a desert island with only a FORTRAN 77 compiler at your disposal, here's a way to write a recursive subroutine.

Simply fortran compiler