Were you used warnings it could be much more easier for you to find reason for your problem.

With warnings turned on your program yeilds warning:

Reference found where even-sized list expected at ...
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for line

c={A=>'0',B=>'0',C=>'0',D=>'0'};
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And with use diagnostics you could get even more detailed explanation of problem:

Reference found where even-sized list expected
 (W misc) You gave a single reference where Perl was
 expecting a list with an even number of elements (for
 assignment to a hash). This usually means that you
 used the anon hash constructor when you meant to use
 parens. In any case, a hash requires key/value pairs.

   %hash = { one => 1, two => 2, };    # WRONG
   %hash = [ qw/ an anon array / ];    # WRONG
   %hash = ( one => 1, two => 2, );    # right
   %hash = qw( one 1 two 2 );          # also fine
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So conclusion is: use strict warnings and diagnostics or die.