using an or statement for multiple items?

[Algar32]

How do I say if grade equals 69 or 79 or 89 etc. I tried using the or symbol but that didnt work (it made the sign a + for every input no matter what). Is there away to do this other than writing out :
if (grade == 69)||(grade==79||(grade==89) etc. etc.
?



here is my actual code:

if (grade == 69,79,89,99,68,78,88,99,100) 
		{
			sign ='+';
		}
			

[Stewbond]

Duplicate of http://cplusplus.com/forum/beginner/64027/

I gave your answer there. Here it is again.

if (grade%10 == 9)
  sign = '+';

You'll need to use a special case for the 100 case:

if (((grade%10 == 9) && (grade > 60)) || (grade == 100))
  sign = '+';

[Algar32]

Thanks for the answer. I didn't see that on the other thread. But this isnt a duplicate, I decided to do it a different way by listing them all out where as before I was trying to make a .at statement do it for me. Thanks.

Also if I did want to list a bunch of numbers like I stated above how would I do it?
Would I have to write them all out like if (grade == 69)||(grade==79||(grade==89) etc. etc.?

[Algar32]

I did it the way you explained and it works great. I guess what I am trying to ask is why doesnt this work?

if (score == 69||79||89||99||68||78||88||99||100) 
		{
			sign ='+';
		}

[Stewbond]

I'm assuming that you are familiar with order of operations in math. (i.e. do () first, then ^, then */, then +-).

There is also an order of operations for C++. See: http://en.cppreference.com/w/cpp/language/operator_precedence

The compiler is first looking at the ==, then it looks at the ||. So things reduce like this:

(score == 69) || 79 || 89 || 99 || 68 || 78 || 88 || 99 || 100
(false|| 79) || 89 || 99 || 68 || 78 || 88 || 99 || 100
(true || 89) || 99 || 68 || 78 || 88 || 99 || 100
(true || 99) || 68 || 78 || 88 || 99 || 100
(true || 68) || 78 || 88 || 99 || 100
(true || 78) || 88 || 99 || 100
(true || 88) || 99 || 100
(true || 99) || 100
(true || 100)
true

The function will always return true.

Here's something that might work for you:

const int plusses[] = {69,79,89,99,68,78,88,98,100};
bool is_plus = false;
for (int i = 0; i < 9; i++)
  if (score == plusses[i]) 
    is_plus = true;
if (is_plus)
  sign = '+';

But that's a bit more complicated than just:
if (score == 69 || score == 79 || score == 89 || ...)

[Algar32]

I understand order of operations I just don't understand why an input for score of say 85 would return true. I understand why it returns true for those values(69,79,89etc.), but I don't understand why it returns true for every value of score.

Sorry if I am kind new to this stuff. You have been very patient with me and I appreciate your help.

[ciphermagi]

@Algar32: (Nice name. I prefer Riva.)

Basically, each side of a logical operator is a complete statement. So if you say:

if(score == 69||79)
Then you're saying 'if score equals 69 or if 79 exists'.

However, if you were to say:

if(score == 69 || score == 79)
Then you're putting a complete statement on both sides of the operator, and it will read as 'if score equals 69 or if score equals 79'.

[Stewbond]

Also remember: true is defined as not zero. So we could also put it like this:
if(score == 69 || 79)
and score is 85 so
if(85 == 69 || 79)
we do the == first (order of operations)
if(false || 79)
and true is anything that is not zero, so 79 is true:
if(false || true)
false || true is true
if(true)

Tada

[Algar32]

So basically anything I line of in those or statements that isnt a zero will get marked as true. So the whole statement will be true as long as one item in the or statement isn't 0.
Thanks guys this helped!

[ciphermagi]

Well, anything that doesn't equal 0 OR evaluate to false (0).