What is this' ! '

It means "not"

It's often used as shorthand for "equal to zero" in C.

 

The world is filled with books like that! I do wonder how many textbooks are ever shown to people who don't know the subject yet, to see if they make any sense before they are printed.

I am afraid that this is about as good as programming jokes get

 

For future reference:

! - NOT, this must be false to continue
!= - NOT equal to N, for comparing non-boolean (numerical) values
== - EQUAL to N, for comparing non-boolean (numerical) values
&& - AND, this AND that = both must be true to continue
|| - OR, this OR that = one or both must be true to continue

% - modulus or mod, aka division returning only the remainder e.g. 17 mod 5 = 2 (2 being the remainder from 17 divided by 5).

For bitwise operations you use only one & and | for "AND" and "OR."

And then if you are doing C++ you use a lot of reference passing which has a & precede an argument in a function call. This just means "here is the address to the beginning of the object or data" which is typ. only 32 bits (4 bytes) in size instead of sending the entire chunk of data as an argument, which can be many, many bytes large.

Code:

	OSErr			theErr = noErr;
	CInfoPBRec 		pBlock; // this is a very large data struct

	memset(&pBlock, 0, sizeof(pBlock));

	...

	theErr = PBSetCatInfoSync(&pBlock);

	if (theErr != noErr) return theErr;

 

That is correct.

Right.

The first. It is only a test in this case. An assignment statement like:

validInput = !validInput;

…would be needed for ! to change the value.

 

lol or there are 10 types of people in this world, those who understand binary and those who dont hahahaha now im a geek too

 

If things make sense, great. Although a lot of this might be a little easier to understand/use if you read up a little on Boolean Algebra. It isn't required reading, and I am pretty sure that a few of the senior programmers in my product area never took classes, but I found that a lot of the logical operators made more sense and were more useful pieces of my programming knowledge once I read up a bit on it. Plus, it helps formalize a bit of the boolean logic used so heavily in expressions. The real only difference is the syntax in C for boolean operators are different then when you write it on paper.

 

! is an operator, just like +, -, *, and /. The ! operator inverts a boolean, so true becomes false, but false also becomes true. An expression like (num == 12) evaluates to a boolean result, so that !(num == 12) is the same as (12 != num).

The if test only looks at the final result after evaluating all expressions inside the parentheses. If this result is true, then the following commands are executed. If it evaluates to false then those commands are skipped.