how do I exclude letters as an input ?

Question

Sarah Sadeq 2016-11-28

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评论： Walter Roberson 2018-3-24

Hello,

I'm working on a project and I'm trying to figure out something and was wondering if someone could help me. I'm asking the user to input positive and non-decimal numbers only. So no strings, no decimals, no negative numbers, no letters, and no blanks.This is my code:

while ( ischar(r) || ischar(c) || isempty(r) || isempty(c))
    disp(' ')
    disp('You have left an answer blank, or entered a non-numeric value.  Please, try again.')
    r = input('enter the next row you wish to explore sire: ');
    c = input('enter the next column you wish to explore sire: ');

When I run it and input in a letter such as a or b..., my code breaks and an error occurs (the error is Undefined function or variable 'a'.). I tried isletter , but still get the same thing. I would appreciate the help!

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Answer 1

Walter Roberson 2016-11-28

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    r = input('enter the next row you wish to explore sire: ', 's');
    c = input('enter the next column you wish to explore sire: ', 's');
    while ~isrow(r) || ~isrow(c) || any(r < '0' | r > '9') || any(c < '0' | c > '9')
      now whine
      and prompt again
    end
    r = str2double(r);
    c = str2double(c);

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Answer 2

the cyclist 2016-11-28

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The issue is that MATLAB evaluates the input. If you just enter a letter (without quotes), then MATLAB evaluates it, can gets an error. This is mentioned in the Description section of the documentation for the input function.

There is a syntax that will read the input as a string, without evaluating it. See the code below. I also had to edit your conditions, to parse out non-empty numeric entries. It's a bit kludgy, but it works. It would not surprise me if there is a more parsimonious way to do this.

r = '';
c = '';
while ( not(isnumeric(str2num(r))) || not(isnumeric(str2num(c))) || isempty(str2num(r)) || isempty(str2num(c)))
    disp(' ')
    disp('You have left an answer blank, or entered a non-numeric value.  Please, try again.')
    r = input('enter the next row you wish to explore sire: ','s');
    c = input('enter the next column you wish to explore sire: ','s');
end

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Julia Hambright 2018-3-24

I am having the issue of matlab not being able to handle a letter input without quotes and I would like to use this code. I was wondering, however, if I am using inputdlg(), then would i define r = ' '; before using inputdlg()? and how will it put a letter into a string if it is being redefined after the user inputs a value Thanks!