Likely default value of an undefined variable

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Are you familiar with the -Wunitialized flag (also included with -Wall) in gfortran?

~/fortran$ cat maybe_uninitialized.f90 
double precision :: gcc, density, ecc
gcc = 2.0d0
density = 1.0d0
ecc    = 1.736d57 * fcc * gcc * density
print *, ecc
end
~/fortran$ gfortran -Wall maybe_uninitialized.f90 
maybe_uninitialized.f90:4:39:

    4 | ecc    = 1.736d57 * fcc * gcc * density
      |                                       ^
Warning: 'fcc' is used uninitialized [-Wuninitialized]
maybe_uninitialized.f90:4:23:

    4 | ecc    = 1.736d57 * fcc * gcc * density
      |                       ^
note: 'fcc' was declared here
  1. Are you using -finit-local-zero in the compilation?
  2. Do you know for certain it runs correctly?
    2.a) What kind of verification and/or validation have you performed?

Compiler-dependent. For a previous discussion see Some type of automatic initialization of variables? - #4 by rwmsu