Invalid expression. Need help fixing my function.

I am new to all of this and cant figure out what it is I am doing wrong. I've been at this for sometime now and I've looked at a lot of reference material and still I have nothing working for me. What error have I made and how can it be fixed? I'm going braindead over here, please and thank you! I've underlined the current trouble spot.

function grade = lettergrade(score)

if score < 0 "OR" score > 100

grade = 'incorrect input';

elseif score <= 90 && score <= 100

grade = 'A';

elseif score >= 80 && score <= 90

grade = 'B';

elseif score >= 70 && score < 80

grade = 'C';

elseif score >= 60 && score < 70

grade = 'D';

elseif score < 60

grade = 'F';

end

Error: File: lettergrade.m Line: 2 Column: 19

Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other syntax error. To construct matrices, use brackets instead of

parentheses.

Answer 1

[Walter Roberson]

if score < 0 || score > 100

[Walter Roberson]

By the way, you do a lot of checking of both bounds, but you do not need to do that.

Suppose you were dealing with integers 1 to 9

if A>=7

that gets 7 8 9

elseif A>=5 && A<7

If you were starting with >= 5 then Yes, that would be 5 6 7 8 9 and in that case the < 7 would filter down to 5 6. But! The 7 8 9 was already consumed by the if before this, and only 1 to 6 are still "available" so you could just test >= 5

[Jacob Smith]

I swear I tryed that already. It sort of worked, I'm not getting any error messages anymore, but my letter grades don't match up with my score inputs.

[Walter Roberson]

Let me put it this way:

Switching to single boundaries like I described in my comment is also a good way to reduce the possibility that you have coded the pair of boundaries incorrectly.

[Jacob Smith]

I think I'm smellin what you're cooking. Thanks for the help.

[Jacob Smith]

Yep, everything is working as it should. Thanks!