while expression specification - problems with error messages

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?

Answer 1

[Walter Roberson]

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

Answer 2

[Azzi Abdelmalek]

abc=input('Choose a number from <-1000;999>: ')  
while abc<-1000 || abc>999
     abc=input('Wrong! Choose again a number from <-1000;999>: ')
     if  isempty(abc)  |  ~isnumeric(abc)
         abc=1000
     end
end

[Walter Roberson]

If you do not include the 's' option for input() then the input is eval()'d. If the user input happens to include a word and that word does not happen to be the name of a variable or function such as pi, then eval() is going to complain about the word being an undefined variable. This is not something you can detect after the fact: the eval() has alredy taken place. So you use the 's' option of input() to receive a string instead.

[Azzi Abdelmalek]

There will be an error message, but the program will not skip the loop. Is there a way to avoid this error message?

[Walter Roberson]

You can use try/catch . But better is to use the 's' option of input() and look at whether you have a number-like-string before you convert the string to numeric.

[John]

Thank you, Azzi. I didn't know about isempty and isnumeric. (I thought it is possible to accept both answers)