How to convert a string to other types (and vice versa) in FORTRAN?
When I was making the DOSCAR tool, I had to convert some data from integer to string. I found that the easiest way is using a character variable as the file name and read or write the I/O list.

Convert a string to another type
read (character_variable, format) list of variables
Convert to a string from another type
write (character_variable, format) list of variables

Example 1:

program integer2string
  integer      :: i
  character*10 :: str
  i = 13
  write(str,'(i0)') i
  write(*,'(a)') trim(str)
  write(str,'(i4)') i
  write(*,'(a)') trim(str)
  write(str,'(i4.4)') i
  write(*,'(a)') trim(str)
end program integer2string

Here is output of the integer2string program:

13
  13
0013

Example 2:

program string2integer
  integer      :: i
  character*10 :: str
  str = '   013   '
  read(str,*) i 
  write(*,'(i2)') i
end program string2integer

Here is output of the string2integer program:

13

Hope it helps!