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How do I check that input is numerical?

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Seán Ó Héir
Seán Ó Héir 2017-4-24
编辑： Stephen23 2023-4-23
I'm trying to create a program that will prompt the user for a numerical input, for example: 'What age are you?'. I know how to prompt the user to ask for an input, but I want to know how to check the answer to make sure it is a numerical figure, ie to stop the user putting in the answer 'twelve'. Any help would be greatly appreciated.
Seán
  1 个评论
Stephen23
Stephen23 2017-4-24
编辑：Stephen23 2017-4-24
More reliable than str2num is to use str2double (which does not call eval and does not evaluate arbitrary code). str2double outputs NaN for invalid input strings, so simply do this:
val = str2double(input('What age are you?','s'));
if isnan(val)
... not a number
else
... was number
end
See KSSV's answer for another example of using str2double.

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采纳的回答

Adam
Adam 2017-4-24
编辑：Adam 2017-4-24
str2num( inputVal )
will return the number if it is valid or empty otherwise so a
if ~isempty( str2num( inputVal ) )
test would check it is a number, or remove the ~ if you want to check for not a number and give an error message in that case.
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Peter
Peter 2023-4-22
I'm a new user, with some help from other answers I found this solution. Option to use existing data from a file or new input; plus checking numeric input, maybe not the best solution, it works
str2num will create error message after input either i or j, compex number
doRun=true;
while doRun=true
disp('input calc_data D1:')
disp('Choose 1 or 2');
disp('1= keep old data');
disp('2= new data');
Sip_choose=input ('Choose 1 or 2: ','s');
option=str2double(Sip_choose);
if(option==1)
calc_data_D1= D1
% old value in mat file saved
break
elseif(option==2)
while doRun
D1=input('=> input calc_data D1= ','s');
D1t=str2double(D1);
TF=isstrprop(D1t,'digit');
if TF==0
D1=D1t;
% new value of D1
doRun=false;
else
disp('no numeric input')
end
end
else
disp('wrong choose of option')
disp('1 or 2 accepted only')
end
end
Stephen23
Stephen23 2023-4-23
编辑：Stephen23 2023-4-23
Ran in:
"so a if ~isempty( str2num( inputVal ) ) test would check it is a number"
Note that STR2NUM is fundamentally buggy:
str = 'struct("x",pi)';
if ~isempty( str2num(str) )
disp('Oh no!')
end
Oh no!
Read the STR2NUM file to understand why. The reliable approach is to use STR2DOUBLE or SSCANF or the like.
@Peter: you can simplify your code by avoiding the conversion to numeric and using STRCMPI.

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更多回答（1 个）

Thorsten
Thorsten 2017-4-24
Using
isnumeric

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