Chaining Bool values give opposite result to expected
boolean, c, c++, compiler-construction, operator-precedence
Solution
`==` groups from left to right, so if all values are zero then:
0 == year // true
(0 == year) == month // false, since month is 0 and (0 == year) converts to 1
((0 == year) == month) == day // true
And so on.
In general, `x == y == z` is not equivalent to `x == y && x == z` as you seem to expect.
Problem
Unthinkingly I wrote some code to check that all the values of a struct were set to 0. To accomplish this I used: ``` bool IsValid() { return !(0 == year == month == day == hour == minute == second); } ``` where all struct members were of type unsigned short. I used the code as part of a larger test but noticed that it was returning false for values differing from zero, and true for values that were all equal to zero - the opposite of what I expected. I changed the code to read: ``` bool IsValid() { return (0 != year) || (0 != month) || (0 != day) || (0 != hour) || (0 != minute) || (0 != second); } ``` But would like to know what caused the odd behaviour. Is it a result of precedence? I've tried to Google this answer but found nothing, if there's any nomenclature to describe the result I'd love to know it. I compiled the code using VS9 and VS8.