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How can I debug this?

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Minhao Wang
Minhao Wang on 25 Sep 2020
Commented: Dana on 29 Sep 2020
clc;clear
C1 = input('Please enter a code to break: ' , 's');
if length(C1) ~= 6
disp('Decoy message: Not a six-digit number.');
else
A = mod(sum(C1 - '0'),2);
if A == 1
disp('Decoy message: Sum is odd.')
else
C2 = (C1(1) - '0') * (C1(2) - '0') - (C1(3) - '0');
failed = false;
switch C2
case 1
Day = 'Rescue on Monday';
case 2
Day = 'Rescue on Tuesday';
case 3
Day = 'Rescue on Wednesday';
case 4
Day = 'Rescue on Thursday';
case 5
Day = 'Rescue on Friday';
case 6
Day = 'Rescue on Saturday';
case 7
Day = 'Rescue on Sunday';
otherwise
disp('Decoy message: Invalid rescue day.');
failed = true;
end
F1 = str2double(C1(4));
F2 = str2double(C1(5));
F3 = str2double(C1(6));
if mod(F1,3) == 0
B = F2 - F3;
else
B = F3 - F2;
end
if ~failed
switch(B)
case 1
Position = ' at the bridge.';
case 2
Position = ' at the library.';
case 3
Position = ' at the river crossing.';
case 4
Position = ' at the airport.';
case 5
Position = ' at the bus terminal.';
case 6
Position = ' at the hospital.';
case 7
Position = ' at St. Petes Church.';
otherwise
disp('Decoy message: Invalid rendezvous point.');
end
disp([Day , Position])
end
end
end
If I enter 918990, I do get what I want, it will show Decoy message: Invalid rendezvous point. But there will appear an error message, how I can debug this?

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Accepted Answer

Dana
Dana on 25 Sep 2020
Edited: Dana on 25 Sep 2020
The error is because if you end up in the "otherwise" case of your switch(B), the variable Position doesn't ever get defined, so when you try to do disp([Day , Position]) it causes an error. To avoid this, you can just put a return statement:
.
.
.
otherwise
disp('Decoy message: Invalid rendezvous point.');
return
end
disp([Day , Position])
end
end
end

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Show 3 older comments
Minhao Wang
Minhao Wang on 29 Sep 2020
Can you please show me how is it done? I am a bit lost to set up a flag in this situation....
Minhao Wang
Minhao Wang on 29 Sep 2020
oh, okay i got it ! thank you !
Dana
Dana on 29 Sep 2020
You already did it once with your failed variable: you set it equal to false initially, and then if you ended up in your "otherwise" case you switched it to true, and then you only proceeded to the switch(B) statement if failed=false. It's exactly the same logic in this case.

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