What would happen if we assign a negative value to a unsigned type in our C code.
Let's look at a example first.if we assigned -1 for the unsigned type,transform -1 to 32 bit binary code is:
1000 0000 0000 0000 0000 0000 0000 0001 (the first number 1 is the symbol of negative value)
when store it in unsigned type, we can simply know it equals 2^31+1.
But the truth is 2^32-1.
And WHY???
It turned out that computer stores a number uses the complement code(补码) rather than true code(原码).while computer know it is a unsigned type value,it will just see this have no symbol bit at the highest position. As for the following code.
1111 1111 1111 1111 1111 1111 1111 1111
So the value of it truly is 2^32-1.
