CATEGORY:
    Chain of blunders (where one blunder leads to another).
    Knuth: Blunder (Thinking the right thing but doing it wrong)

REFERENCE:
    https://www.tug.org/TUGboat/tb10-4/tb26knut.pdf

EXPLANATION:
    The forward declaration of PRIME_TABLE in prime_table.h lacks an 'extern'
    specifier:

    // prime_table.h
    const unsigned int PRIME_TABLE[10];

    Since the unlucky author of the Makefile also forgot to link the
    prime_table.o object file to the executable:

    # Makefile
    prime_sum : prime_sum.o

    the real, intended array definition with the desired prime numbers is
    missing. According to the C language standard [1], a declaration that is
    not followed by a definition becomes the de facto definition.

CONSEQUENCES:
    Since the de facto definition of PRIME_TABLE is not explicitily
    initialized, it's zero-initialized by the compiler. As a result, the
    program will sum-up 10 zeros and hence output zero as the result.

BUGFIX:
    Declaring PRIME_TABLE 'extern' in prime_table.h:

    extern const unsigned int PRIME_TABLE[10];

    makes the blunder in the Makefile immediately obvious:

    gcc -Wextra -Wall -pedantic -ansi-c -o prime_sum.o prime_sum.c
    gcc  prime_sum.o prime_table.h -o prime_sum
    prime_sum.o: In function `main':
    prime_sum.c:(.text+0x25): undefined reference to `PRIME_TABLE'

    Fixing the Makefile is trivial:

    # Now contains prime_table.o as well:
    prime_sum : prime_sum.o prime_table.o

REMARKS:
    * This bug could not have happened in C++ as definitions of constants
      without explicit initialization values are considered illegal.

    * clang supports the -Wmissing-variable-declarations warning that is able
      to catch this bug:

      prime_table.h:4:20: warning: no previous extern declaration for
      non-static variable 'PRIME_TABLE' 

      Unfortunately, this warning is disabled by default and neither part of
      -Wall nor -Wextra.

NOTES:
    [1] Refer to ISO C99 standard, 6.9.2 External object definitions:

    A declaration of an identifier for an object that has file scope without an
    initializer, and without a storage-class specifier or with the
    storage-class specifier static, constitutes a tentative definition. If a
    translation unit contains one or more tentative definitions for an
    identifier, and the translation unit contains no external definition for
    that identifier, then the behavior is exactly as if the translation unit
    contains a file scope declaration of that identifier, with the composite
    type as of the end of the translation unit, with an initializer equal to 0.