logical-operators

This question already has an answer here: What does !!(x) mean in C (esp. the Linux kernel)? 3 answers I've seen code where people have used conditional clauses with two '!'s #define check_bit(var, pos) (!!((var) & (1 << (pos)))) #define likely(x) __builtin_expect(!!(x),1) #define unlikely(x) __builtin_expect(!!(x),0) are some of the examples I could find. Is there any advantage in using !!(condition) over (condition) ? Well if the variable you are applying !! is not already a bool ( either zero or one ) then it will normalize the value to either 0 or 1 . With respect to __builtin_expect this

In C++, is there any difference between doing && (logical) and & (bitwise) between bool(s)? bool val1 = foo(); bool val2 = bar(); bool case1 = val1 & val2; bool case2 = val1 && val2; Are case1 and case2 identical or if not how exactly do they vary and why would one choose one over the other? Is a bitwise and of bools portable? The standard guarantees that false converts to zero and true converts to one as integers: 4.7 Integral conversions ... If the destination type is bool, see 4.12. If the source type is bool, the value false is converted to zero and the value true is converted to one. So

I read the following Stack Overflow questions, and I understand the differences between bitwise and logical. Difference between & and && in PHP Reference - What does this symbol mean in PHP? However, none of them explains when I should use bitwise or logical. When should I use bitwise operators rather than logical ones and vice versa? In which situation do I need to compare bit by bit? I am not asking about the differences, but I am asking the situation when you need to use bitwise operators. Bitwise | and & and logical || and && are totally different . Bitwise operators perform operations on

#include <iostream> using namespace std; int main(int argc, char *argv[]) { int i=-5; while(~(i)) { cout<<i; ++i; } } The output is -5,-4,-3,-2. Shouldn't it print values till -1?Why is it only till -2. And please explain me the difference between 'not' and 'negation' operators.When ever I write a program they were the source for bugs. while(i) I know that the loop condition will be true for positive and negative i's except 0. while(!i) vs while(~i) For what values of 'i' the above two loops get executed? When i gets to -1 , the value of ~i is ~-1 , or 0 , so the while loop stops executing.

I personally like the exclusive or , ^ , operator when it makes sense in the context of boolean checks because of its conciseness. I much prefer to write if (boolean1 ^ boolean2) { //do it } than if((boolean1 && !boolean2) || (boolean2 && !boolean1)) { //do it } but I often get confused looks from other experienced Java developers (not just the newbies), and sometimes comments about how it should only be used for bitwise operations. I'm curious as to the best practices regarding the usage of the ^ operator. You can simply use != instead. I think you've answered your own question - if you get

I have this simple line of code: i = " " if i != "" or i != " ": print("Something") This should be simple, if i is not empty "" OR it's not a space " " , but it is, print Something. Now, why I see Something printed if one of those 2 conditions is False ? De Morgan's laws , "not (A and B)" is the same as "(not A) or (not B)" also, "not (A or B)" is the same as "(not A) and (not B)". In your case, as per the first statement, you have effectively written if not (i == "" and i == " "): which is not possible to occur. So whatever may be the input, (i == "" and i == " ") will always return False and

I have read http://stat.ethz.ch/R-manual/R-devel/library/base/html/Logic.html and the difference between & and && doesn't make sense. For example : > c(1, 2, 3) & c(1,2,3) [1] TRUE TRUE TRUE According to the link this is expected behavior. It is doing an element-wise comparison of the two vectors. So I test again... > c(1, 2, 3) && c(1,2,3) [1] TRUE This also returns what was expected. But then I change a value... > c(1, 2, 3) && c(1,3,3) [1] TRUE Still expected because it short circuits on the first element. > c(1, 2, 3) & c(1,3,3) [1] TRUE TRUE TRUE This however lost me. These two vectors

I am wondering what the exclamation mark in if(!anObject) means. It is the boolean NOT operator also called negation. !true == false; !false == true; That is the Logical NOT operator, i.e., if( thisThisIsNotTrue ) { doStuff } . It's a C operator, simply meaning "not". So !YES == NO and !NO == YES are both true statements. if (![txtOperator.text isEqualToString: @"+"]) , for example, checks to see if txtOperator.text is NOT equal to @"+". If it always adds, then your string is never "+". The logic as you have it will always add a+b unless the txtOperator.txt is exactly equal to @"+".

After I run the code in matlab, I encounter this error and unsure how to solve it. How can I solve this problem. Warning: Operands to the || and && operators must be convertible to logical scalar values. Jgray = double(rgb2gray(J)); % Calculate the Gradients [dIx, dIy] = gradient(Jgray); if max(dIx)<=103 && max(dIy)<=100 B = abs(dIy) - abs(dIx); else B = abs(dIx) - abs(dIy); end user1083059 If dIx and dIy are matrices (as opposed to 1-D vectors), max(dIx) and max(dIy) will return vectors. && and || should be used to compare scalars, not vectors. You probably want to type if max(dIx(:))<=103 &&