Unsigned int reverse iteration with for loops

Question

I want the iterator variable in a for loop to reverse iterate to 0 as an unsigned int, and I cannot think of a similar comparison to i > -1, as

Answer 1

for(unsigned i = x ; i != 0 ; i--){ ...

And if you want to execute the loop body when i == 0 and stop after that. Just start with i = x+1;

BTW, why i must be unsigned ?