Hi,

If you want to call a variable in main program from subroutine, you have to declare that variable as global and use that global for subroutine and main program. Otherwise, you will get the problem likesh your question.

Dear Mr. @Syahril Siregar

I am grateful for your time, but the problem is I want to call variable from main into a subroutine, not from subroutine into main. The thing which teases me the most is that I am calling almost 5 variables from the main program to be used in the subroutine, four are fine while only one changes its value to zero.

What are the data types of the variable and the formal argument? If you pass a positive integer and the formal argument is real you will usually get a value very close to zero.

Dear @John Collins

Thanks for your answer. In fact the data type of my variable is real and I have declared it both in the main and the subroutine.

It is very difficult to meaningfully diagnose issues like this without being able to actually see the code in question (ideally a reduced test case exhibiting the unexpected behaviour), and a description is usually woefully insufficient since, if the underlying issue is a misconception of the programmer, the description will simply echo the misconception instead of what the code is actually doing.

If you can share some (trimmed) code (e.g. Github Gist, Pastebin), it should be straightforward to point out the problem; but in absence thereof my best guess is that you're confused in some way about Fortran's scoping rules.