What is the purpose of “int mask = ~0;”?

Question

I saw the following line of code here in C.

 int mask = ~0;

I have printed the value of mask in C and C++. It always prints

Answer 1

Loooong ago this was how you saved memory on extremely limited equipment such as the 1K ZX 80 or ZX 81 computer. In BASIC, you would

Let X = NOT PI

rather than

LET X = 0

Since numbers were stored as 4 byte floating points, the latter takes 2 bytes more than the first NOT PI alternative, where each of NOT and PI takes up a single byte.