在while语句中理解逻辑表达式

Question

I have code that reads numbers from keyboard and sums them and outputs the sum when the loop terminates. The loop terminates when the number inputed is negative and divisible by 2 or it is positive and divisible by 3. But it is not working correctly. Where is the problem in the while condition?

while(!(n<0 && n%2==0) || !(n>0 && n%3==0))

Answer 1

This is related to the negating logical expressions. The most simple way is to write a positive expression and the negate it with ! :

!((n<0 && n%2==0) || (n>0 && n%3==0))

After that you can open the parentheses using Boolean algebra rules: when you open a negation statement you add a negation before each component and replace OR with AND and vice versa:

!(n<0 && n%2==0) && !(n>0 && n%3==0)

Using this rule you can continue opening the parentheses.

Answer 2

!(n<0 && n%2==0) || !(n>0 && n%3==0)

NOT (n is negative AND n is divisible by 2) OR NOT (n is positive AND n is divisible by 3).

This is a logical error NOT (A OR B) is not the same as (NOT A or NOT B), it is equal to NOT A and NOT B.

Check out: http://integral-table.com/downloads/logic.pdf