I need to know why my While Loop is breaking

I have the following code. My problem is that once I enter a negative number two consecutive times, instead of repeating the actions within the while loop, the program crashes by giving me an error. Why is this the case and what can I do to remedy my problem?

P=inputdlg('Enter a numeric value for an initial amount of money');
P=cell2mat(P); 
P=str2num(P);

while P<0 || ~isnumeric(P)
   errordlg('You have made an invalid entry! Please try again.');
   P=inputdlg('Enter a numeric value for an initial amount of money');
   continue;
end

Answer 1

[Image Analyst]

This works:

P = -1;
while P<0
  caUserInput = inputdlg('Enter a positive numeric value for an initial amount of money');
  if isempty(caUserInput),return,end; % Bail out if they clicked Cancel.
  % Convert to floating point from string.
  usersValue = str2double(caUserInput{1})
  % Check for a valid integer.
  if isnan(usersValue)
    % They didn't enter a number.
    % They clicked Cancel, or entered a character, symbols, or something else not allowed.
    message = sprintf('I said it had to be a positive number!');
    uiwait(warndlg(message));
  else
    % Else the entry is okay.
    P = usersValue;
    % But check if it's negative.
    if P < 0
      message = sprintf('I said it had to be a positive number!');
      uiwait(warndlg(message));
    else
      break;
    end
  end
end
uiwait(msgbox('Done with while loop'));