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How to detect negative number in Switch and case statement

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I want to implement some control actions based on the sign of the error and Uz.
when error = -1, Uz = -1.
The output is 'other value' instead of 'Object losing altitude'.
Please how can I correct it.
Thank you for the help.
error = -1;
Uz = -1;
switch error
case error > 0 && Uz > 0
disp('Controller should not take any action')
case error > 0 && Uz < 0
disp('Open the control valve and supply more lifting gas')
case error < 0 && Uz < 0
disp('Object losing altitude')
otherwise
disp('other value')
end

Accepted Answer

Scott MacKenzie
Scott MacKenzie on 10 Aug 2021
Look carefully. Because you are switching on error, your first case expression reduces to
error == (error < 0 && Uz > 0)
which is false. In fact, all your case expressions are false so the otherwise statement always executes.
The fix: Just use an if-else arrangement:
error = -1;
Uz = -1;
if error > 0 && Uz > 0
disp('Controller should not take any action')
elseif error > 0 && Uz < 0
disp('Open the control valve and supply more lifting gas')
elseif error < 0 && Uz < 0
disp('Object losing altitude')
else
disp('other value')
end
Object losing altitude
  1 Comment
Telema Harry
Telema Harry on 10 Aug 2021
Thank you for the feedback @Scott MacKenzie.
I was intentionally avoiding the if statement as I have up to 10 different conditions and the switch statement is easier to read. I will just stick with the if statement.
thanks for the help.

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