This is why Unix is case sensitive. The variables chChar and chchar are not the same. For most processors this brings no speed penalty. It will probably be slower to have single precision variables and have to recast the double precision function values to single precision. There are two other integer types, although these are of lesser value in large-scale scientific calculations.
Integers can also be short, and unsigned.
There are no complex variables, although I have never had to use complex numbers in 28 years of coding Fortran. There are two main classes, local and global namespace. A local variable is redefined from the stack when this part of a code is entered. N.B., few Fortran compiler actually use stack memory, and save statements are not important. All the C compilers I have seen take this very seriously - variable values will be volatile and lost if not declared static.