Numeric Data Validation While Loop in Matlab - matlab

Question

I have a function usenum
function TF = usenum(x)
TF = false;
if ~isnumeric(x)
h = msgbox('Input is not numeric');
elseif (x <= 0)
h = msgbox('Input must be > 0');
else
TF = true;
end
I am getting user input in the main menu:
answer = inputdlg(prompt,dlg_title,num_lines,def);
The inputdlg has 2 values and can be indexed by {1} and {2}
I want to wait for the user to input a value, the value has to be a number and greater than 0. in the case that he doesn't, I want to output the respective message and make him keep inputting until he gets it right, or close the inputdlg dialog.
I am attempting something like this:
condition = false;
while ~condition
answer = inputdlg(prompt,dlg_title,num_lines,def);
numOfTracks = answer{1};
bpmRange = answer{2};
condition = usenum(numOfTracks);
end
I am trying to say, while condition = false, i.e. while input is not numeric or not greater than 0, keep getting user input. Once the user inputs a valid number the condition is supposed to become true and the while is supposed to terminate. However, the inputdlg keeps opening for input and the only way I can stop it is by closing it (infinite loop). how can I achieve what I want?
Thanks in advance

Answer 1

Your loop appears to be correct. The following testing provides results of your usenum function.
>> usenum('')
ans =
0
>> usenum(-1)
ans =
0
>> usenum(1)
ans =
1
Your usenum function is correct as far as typing is concerned, but I believe your input is always given as a string since you're getting user input from a dialogue. Instead, you should try redefine usenum as follows if you're expecting a string input. The function str2double converts it to a double and if it's text, it will show as NaN. That's what the isnan check is for, to check if it's text.
function TF = usenum(x)
% Default to false
TF = false;
x = str2double(x);
% Check if digits
if isnan( x )
h = msgbox('Input is not numeric');
elseif (x <= 0)
h = msgbox('Input must be > 0');
else
TF = true;
end
This is the result of the new function.
>> usenum('a')
ans =
0
>> usenum('-1')
ans =
0
>> usenum('1')
ans =
1