How to create a user defined function that contain if else function. Can I create a user function from the line e line %user defined function

%menu for user to choose

disp('Convert between Celcious and Fahrenheit');

disp('Choose a number:');

disp('1.Celcious to Fahrenheit');

disp('2.Fahrenheit to Celcious');

%input

choice = input("\nInput:",'s');

while (strcmpi(choice, '1') == 0 && strcmpi(choice, '2') == 0)

disp('Choose number 1 or 2');

choice = input("\nInput: ",'s');

end

%user defined function

if (choice == '1')

cel = input("\nEnter temperature in Celcious to convert to Ferenheit:");

while (cel < 0)

disp('Enter a positive number, please');

cel = input("\nEnter temperature in Celcious to convert to Ferenheit:");

end

if (cel >= 0)

cel2fa = (cel*1.8) + 32;

fprintf('Coverted: %.2f Fahrenheit \n',cel2fa);

end

end

if (choice == '2')

fa = input('\nEnter temperature in Ferenheit to convert to Celcious:');

while (fa < 0)

disp('Enter a positive number, please');

fa = input("\nEnter temperature in Celcious to convert to Ferenheit:");

end

if (fa >= 0)

fa2cel = (fa-32)/1.8;

fprintf('Coverted: %.2f Celcious \n',fa2cel);

end

end

Answer 1

[DGM]

Well, you can certainly make it into a function:

clearvars; clc;

% the user is never told the meaning of what they're selecting
disp('Choose number 1 or 2');
choice = input("\nInput: ",'s');
while ~ismember(choice,{'1','2'})
	choice = input("\nInput: ",'s');
end
myfunction(choice); % call the function

% ----------------------------------------------------------------
% it's a function now i guess
function myfunction(choice)
	switch choice
		case '1'
			cel = input("\nEnter temperature in Celcious to convert to Ferenheit:");

			% why restrict the functionality to positive numbers only?
			% the math works for negatitve numbers too
			while (cel < 0)
				disp('Enter a positive number, please');
				cel = input("\nEnter temperature in Celcious to convert to Ferenheit:");
			end
			% what is the utility of formatted text output dumped directly to console?
			if (cel >= 0)
				cel2fa = (cel*1.8) + 32;
				fprintf('Coverted: %.2f Fahrenheit \n',cel2fa);
			end

		case '2'
			fa = input('\nEnter temperature in Ferenheit to convert to Celcious:');

			while (fa < 0)
				disp('Enter a positive number, please');
				fa = input("\nEnter temperature in Celcious to convert to Ferenheit:");
			end
			if (fa >= 0)
				fa2cel = (fa-32)/1.8;
				fprintf('Coverted: %.2f Celcious \n',fa2cel);
			end

	end
end

... but I don't know that it improves much.

I know this is probably just homework, and the structure is stipulated by the given assignment. This pattern of prompting the user interactively for every input is just bad design, and I don't know why instructors love teaching it. It has no programmatically-useful inputs or outputs, and the fact that it relies on direct human interaction for all I/O means it's optimized for being tedious and prone to human error.

If you wanted a more practical function that did temperature conversions, you'd consider efficiency and flexibility of both the code and the usage. Where to start? The function only needs one numeric input and something that tells it what conversion to make. Decide on a convenient syntax and go. Get all the inputs first, convert the number, and prepare the outputs.

function varargout = tempconverter(tempin,convstring)
%  TEMPOUT = TEMPCONVERTER(TEMPIN,CONVERSIONTYPE)
%  blah blah blah this describes the function behavior and usage
%
%  TEMPIN is a number (scalar or array)
%  CONVERSIONTYPE is one of the following:
%     'ctof' for Celsius to Farenheit
%     'ftoc' for Farenheit to Celsius
%
%  If called with scalar input and no output argument, 
%  a textual description of the conversion will be printed.
%
% See also: convtemp

switch lower(convstring)
	case 'ftoc'
		tempout = (tempin-32)*5/9;
	case 'ctof'
		tempout = 32 + (tempin*9/5);
	otherwise 
		error('TEMPCONVERTER: invalid conversion type %s',convstring)
end

if nargout == 0 && isscalar(tempin)
	switch lower(convstring)
		case 'ftoc'
			fprintf('%.2f°F is equal to %.2f°C\n',tempin,tempout)
		case 'ctof'
			fprintf('%.2f°C is equal to %.2f°F\n',tempin,tempout)
	end
else
	varargout{1} = tempout;
end

The above function will provide conversion for scalars or arrays, and if called with no outputs, it will do pretty formatted output just for reading.

tempconverter(200,'ftoc')

200.00°F is equal to 93.33°C

T = tempconverter([100 25 0 -40],'ctof')

T = 1×4

212 77 32 -40

The comment block at the top of the function is the help synopsis and describes the usage so that the user knows what they're doing instead of being asked to blindly pick a number. Writing this first may help you decide what syntax will be convenient.

help tempconverter

   TEMPOUT = TEMPCONVERTER(TEMPIN,CONVERSIONTYPE)
   blah blah blah this describes the function behavior and usage
 
   TEMPIN is a number (scalar or array)
   CONVERSIONTYPE is one of the following:
      'ctof' for Celsius to Farenheit
      'ftoc' for Farenheit to Celsius
 
   If called with scalar input and no output argument, 
   a textual description of the conversion will be printed.
 
  See also: convtemp

If you wanted to add a new conversion to that example, all you'd need is one new line in the synopsis, and one new case in each of the two switch-case structures -- 5 lines. It could definitely be simpler than that, but it's a start toward reducing repeated code.

That said, I'm sure that this example doesn't directly satisfy the requirements of your assignment, but you're free to use it directly or conceptually to make something that does.

[Minh Hien Nguyen]

Actually you solve my problems. What I wonder is how to call a function that have if else inside a switch case since I thought we need to list out all the input

[DGM]

I don't know what you mean about listing the input. Was that a requirement of the assignment?

If you're asking about the lack of input() calls in the second example I gave, it doesn't use interactive prompts at all. It would be called directly with the desired parameters as shown.