Rename your file from First.f to First.f90. You have encountered an issue which is easily avoided. Compilers generally assume that .f files are written in what is known as fixed source form, which has been obsolescent since Fortran 90. With the .f90 suffix your compiler should expect to encounter free source form and not complain … Read more
If you have a Fortran 2003 compiler, the intrinsic module iso_fortran_env defines the variables input_unit, output_unit and error_unit which point to standard in, standard out and standard error respectively. I tend to use something like #ifdef f2003 use, intrinsic :: iso_fortran_env, only : stdin=>input_unit, & stdout=>output_unit, & stderr=>error_unit #else #define stdin 5 #define stdout 6 … Read more
The implicit statement (including implicit none) applies to a scoping unit. Such a thing is defined as BLOCK construct, derived-type definition, interface body, program unit, or subprogram, excluding all nested scoping units in it This “excluding all nested scoping units in it” suggests that it may be necessary/desirable to have implicit none in each function … Read more
As indicated in comments, real*8 isn’t standard Fortran. This FAQ entry has more details. That said, once we’re into the non-standard realm… The 8 refers to the number of bytes that the data type uses. So a 32-bit integer is integer*4 along the same lines. (But is also non-standard.) A quick search found this guide … Read more
According to The Fortran 2003 Handbook by Adams, et al., there is one difference between an intent(inout) argument and argument without specified intent. The actual argument (i.e., in the caller) in the intent(inout) case must always be definable. If the intent is not specified, the argument must be definable if execution of the subroutine attempts … Read more
In principal when a module goes out-of-scope, the variables of that module become undefined — unless they are declared with the SAVE attribute, or a SAVE statement is used. “Undefined” means that you are not allowed to rely on the variable having the previous value if you again use the module — it might have … Read more
The KIND of a variable is an integer label which tells the compiler which of its supported kinds it should use. Beware that although it is common for the KIND parameter to be the same as the number of bytes stored in a variable of that KIND, it is not required by the Fortran standard. … Read more
Fortran is, for better or worse, the only major language out there specifically designed for scientific numerical computing. It’s array handling is nice, with succinct array operations on both whole arrays and on slices, comparable with matlab or numpy but super fast. The language is carefully designed to make it very difficult to accidentally write … Read more
In Fortran >=90, the best approach is use intrinsic functions to specify the precision you need — this guarantees both portability and that you get the precision that you need. For example, to obtain integers i and my_int that will support at least 8 decimal digits, you could use: integer, parameter :: RegInt_K = selected_int_kind … Read more
This style ensures that the maximum precision available on ANY architecture is used when assigning a value to PI.