Fortran – Subroutines and Iteration

I used the registered version of the Simply Fortran compiler, here: simplyfortran-3.0.msi, simplyfortran-2.35.msi; also, try the online Fortran compiler.

PROGRAM MAIN

! inhibit older feature
IMPLICIT NONE
    
    ! declare numbers    
    INTEGER N, X
    
    ! declare sub    
    EXTERNAL SUB1
    
    ! declare global variable
    COMMON /GLOBALS/ N
    
    ! set initial value
    X = 0
    
    ! input how many interations
    PRINT *, 'Enter number of interations: '
    READ (*,*) N
    
    ! goto sub1
    CALL SUB1(X,SUB1)
    
    ! end program
    END

    ! our sub
    SUBROUTINE SUB1(X,LOOP)
        INTEGER N, X
        EXTERNAL LOOP
        COMMON /GLOBALS/ N
    
        IF(X .LT. N)THEN
            X = X + 1
            PRINT *, 'x = ', X
            CALL LOOP(X,LOOP)
        END IF
        ! end if
    
    ! end sub
    END

 

Output

 

Notes

Learn more, Fortran language

https://pinetools.com/syntax-highlighter

 

Types of Variables

Integer: It can hold only integer values.

Real: It stores the floating point numbers.

Complex: It is used for storing complex numbers.

Logical: It stores logical Boolean values.

Character: It stores characters or strings.