I have a question about overflow. This is problem that converting to 8 bit two's complement number or indicate that the decimal number would overflow the range. my question is why decimal number or 128 is overflow but why -128 is not? also why

I have a question about overflow.

This is problem that converting to 8 bit two's complement number or indicate that the decimal number would overflow the range.

my question is why decimal number or 128 is overflow but why -128 is not?

also why -59 is overflow too? And also what if the problem is converting to 8 bits sign/magnitude numbers in this cases?

plz explain all the details..