Negative numbers are stored as 2's complement in memory, how does the CPU know if it's negative or positive?

Question

-1 can be represented in 4 bit binary as (2\'s complement) 1111

15 is also represented as 1111.

So, how does CPU differentiate between 15 and -1 when it get

Answer 1

At the compiler level, the differentiation is based on data type. If the data type is int, then 4 bytes is allocated to that variable (in C). So 15 in 2's complement is 00000000 00000000 00000000 00000000 00001111 while -1 is 11111111 11111111 11111111 11111111 . The compiler then converts this to the corresponding opcode of the CPU. The CPU executes this opcode and at this level everything is in the form of 1s and 0s.