inputdlg - how do i recognise if someone entered a symbol, e.g. = into the box?

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how do i recognise if someone entered a symbol, e.g. = into the box?
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Dominique Joubert
Dominique Joubert le 22 Août 2018
i want a user to enter the right side of an equation:for example s+2*a-3/r
Stephen23
Stephen23 le 22 Août 2018
Modifié(e) : Stephen23 le 22 Août 2018
What about all of the ASCII control characters, i.e. char(0:31)? What about non-breaking spaces, en dashes, em dashes, etc?
There are many characters that you are likely to want to exclude, and building a list of them all is intractable. It would be much easier to define what characters are allowed, as this list will be much smaller. For that you can use a regular expression.
Note that writing a language parser is not a trivial task.

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Niklas Nylén
Niklas Nylén le 22 Août 2018
Verifying that the expression is a valid equation is probably extremely hard, but validating that only "allowed" symbols are entered is quite simple using regexp:
% Allowing +, -, *, / and space. Expand list if needed.
validSpecialChars = regexptranslate('escape', '+-*/ ')
assert(isempty(regexp(input, ['[^A-Za-z0-9' validSpecialChars ']'], ...
'Expression %s contains invalid characters', input)

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