Using nargin for a menu function

I have a menu function with 4 choices. The first two are buttons to be pressed to enter a start date (choice 1) and an end date (choice 2). Choice 3 cancels the script (it is in a while loop), and choice 4 continues with the dates selected to plot some functions. I want to add code that says "if a start date wasn't chosen, Start_Date1 = datetime('now') - 14" and "if an end date wasn't chosen then End_Date1 = datetime('now') + 1". I tried to do this with the following code for choice 1 of the menu. However, it doesn't work when I run the program and don't select a start or end date manually. When I run it in debug mode, by executing each line at a time in the command window it works... Does anybody know what the issue is? (Note: the code is the same for choice 2 on the menu, except with End_Date1.)

   if nargin < 1
     Start_Date1 = datetime('now') - 14; 
     Start_Date1 = dateshift(Start_Date1,'start','day');
     day1 = datenum(Start_Date1);
   end

[Geoff Hayes]

Kyle - please provide some context for the above code. What is the function for it? A callback? Or is this just in your while loop as

 while true
     % do stuff
     % read menu choice
     % etc.
     if nargin < 1
         % etc.
     end
 end

What function does the nargin correspond to?

[Walter Roberson]

There are different ways to implement that kind of menu. Please show your code

[Kyle Reagan]

The function itself is quite long, but the part corresponding to the menu is within a while true argument as seen below. Let me know if you need more information about it. Note that once choice 4 is chosen, the MyCO2plotter continues the script and plots data (code not seen below).

function MyCO2plotter

% First Menu
continueprogram = true;
    while continueprogram
    choice = menu('CO2 Plotting Tool','Enter Start Date','Enter End Date','Cancel','Plot Data'); 
        switch choice
            case 1
                % Case for entering start date
                day1 = uigetdate;
                day1 = floor(day1); % This is becuase uigetdate starts at the hour and minute of the day you use it on
                Start_Date = datestr(day1);
                Start_Date1 = datetime(Start_Date); % Changes from character to variable
                fprintf('Start Date: %s \n', Start_Date)

                  % Set start day to 2 weeks back if no date is chosen.
                  if nargin < 1
                      Start_Date1 = datetime('now') - 14; 
                      Start_Date1 = dateshift(Start_Date1,'start','day');
                      day1 = datenum(Start_Date1);
                      fprintf('Start Date: %s \n', Start_Date)
                  end

              case 2
                  % Case for entering end date
                  day2 = uigetdate;
                  day2 = floor(day2);
                  End_Date = datestr(day2);
                  End_Date1 = datetime(End_Date);
                  fprintf('End Date: %s \n', End_Date)
                      if day2 < day1
                          continueprogram = false;
                          clear
                          clc
                          fprintf('Error. The end date must be after the start date. Restart program and enter dates correctly. \n')
                      end

                  % Set end day to tomorrow if no date is chosen.
                  if nargin < 1
                      End_Date1 = datetime('now') + 1;
                      End_Date1 = dateshift(End_Date1,'start','day');
                      day2 = datenum(End_Date1);
                      fprintf('End Date: %s \n', End_Date)
                  end

              case 3
                  % Cancels menu feature
                  continueprogram = false;
                  clearvars -global;
                  clearvars;
                  clc;

              case 4 % Plots data   
                  continueprogram = false;

          end
      end

[Adam]

nargin is for arguments. Your code doesn't appear to be using a function where arguments are passed in.

I assume uigetdate returns [] or 0 or something like that if it is closed without a date selection which I assume is what you mean by no date selected. So just use that in a test.

The location of your code is confusing though because you have 4 lines of code that assume a date was chosen before you then try to handle the case of a date not being chosen, unless I am reading your code incorrectly.

Answer 1

[Walter Roberson]

function MyCO2plotter

    % Initialize start day to 2 weeks back
    Start_Date1 = datetime('now') - 14; 
    Start_Date1 = dateshift(Start_Date1,'start','day');
    day1 = datenum(Start_Date1);
    fprintf('Start Date: %s \n', Start_Date)

    % Initialize end day to tomorrow

    End_Date1 = datetime('now') + 1;
    End_Date1 = dateshift(End_Date1,'start','day');
    day2 = datenum(End_Date1);
    fprintf('End Date: %s \n', End_Date)

    % First Menu
    continueprogram = true;
    while continueprogram
      choice = menu('CO2 Plotting Tool','Enter Start Date','Enter End Date','Cancel','Plot Data'); 
          switch choice
              case 1
                  % Case for entering start date
                  day1 = uigetdate;
                  day1 = floor(day1); % This is becuase uigetdate starts at the hour and minute of the day you use it on
                  Start_Date = datestr(day1);
                  Start_Date1 = datetime(Start_Date); % Changes from character to variable
                  fprintf('Start Date: %s \n', Start_Date)

                case 2
                    % Case for entering end date
                    t_day2 = uigetdate;
                    t_day2 = floor(t_day2);
                    t_End_Date = datestr(t_day2);
                    t_End_Date1 = datetime(End_Date);

                    if t_day2 < day1
                      fprintf('Error. The end date must be after the start date. Try again.\n');
                    else
                      day2 = t_day2;
                      End_Date = t_End_Date;
                      t_End_Date1 = t_End_Date1;
                      fprintf('End Date: %s \n', End_Date)
                    end

                case 3
                    % Cancels menu feature
                    continueprogram = false;

                case 4 % Plots data
                    %you probably want to plot at this point   
                    continueprogram = false;
            end
        end

[Kyle Reagan]

Thanks Walter, I was actually just about to comment that I did this (instead of messing with nargin) and saw that you had suggested the same thing. Works like a charm, thanks to all for the help.