How do I check that input is numerical?
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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
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.
采纳的回答
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.
4 个评论
Seán Ó Héir
2017-4-24
Adam
2017-4-24
Yeah, sorry, it was a quick answer and I chose a very bad variable name. I've edited it now. the argument to str2num was just meant to be your variable that you have extracted from the prompt, not a call to the 'input' function.
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
"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
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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