MATLAB: While expression specification – problems with error messages

errorexpressionwhile

Hello,
is there any (simple) way to set up that an input can contain ONLY values from an interval (not necessarily of integers)?
Something such as:
abc=input('Choose a number from <-1000;999>: ')  
while abc<1000||abc>999
       abc=input('Wrong! Choose again a number from <-1000;999>: ')
works good, when I answer outside the interval. However, when I answer with a letter or with nothing typed at all – just clicking on enter button, I get these error messages:
??? Error using ==> input
Undefined function or variable '_that letter_'.
or
??? Error: Unexpected MATLAB expression.
for the letters. And:
??? Operands to the || and && operators must be convertible to logical scalar values.
Error in ==> blah at 12
while abc<-1000||abc>999
while no typing an answer at all. I want to make it idiotproof as much as possible.
I guess I am not even taking into account typing more inputs (probably nargin>1; error('… :'?). That could actually sort out the latter, too via nargin<1, right?

Best Answer

If you wish to be able to detect and smoothly handle letters in input, you need to use
abc_string = input('Choose a number from <-1000;999>: ', 's');
and then you have to figure out whether the string in abc_string looks like a number or not and then convert it to a numeric value.
Note: your current code has
while abc<1000||abc>999
but the beginning of your range is negative so you would want
while abc<-1000||abc>999
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