C:\>perl -E "my $c; open(IN,"$c-assignments.dat") or die "Can't open input: $!\n";
Can::t at -e line 1.

C:\>perl -E "my $c; open(IN,\"$c-assignments.dat\") or die \"Can't open input: $!\n\""
Can't open input: No such file or directory

C:\>perl -E "my $c; say $c - assignments.dat;"
0dat

C:\>perl -E "my $c; say $c-assignments.dat;"
0dat

C:\>perl -E "my $c; say \"$c-assignments.dat\";"
-assignments.dat