"HREAD" is used but not declared"-Read text image data Error

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Yes, you can only run the testbench in modelsim. Textio is not appropriate for synthesys, hence why you cannot compile in Quartus.

The error you are getting is a type missmatch, you probably need to convert them using the to_signed(int, size) function.

If you are unfamiliar with this, and textio, I suggest you read some VHDL tutorials, as these are very basic parts of VHDL.

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Did you mean I need to convert constant Ce that includes all the alphabet to signed? Thanks for your concern Tricky!