how do I get only 1 variable passed through a function?

Hi I only want to either r or a,b to show if case 1 or case 2 is chosen but MATLAB returns unrecognized variable a,b if r is chosen and vice versa, how do I only have one variable chosen to be passed through the function?

fprintf('Enter either circle (1) or ellipse (2):\n')
choice = input('','s')

switch choice;
    case '1'
        fprintf('What is the circle''s radius?\n')
        r = input(' ');
    case '2'
        fprintf('What is the ellipse''s minor and major axis lengths?\n')
        a = input('Minor length: ');
        b = input('Major length: ');
    otherwise 
        fprintf('Please enter either [1] or [2]');
end

[C,E] = circumference(r,a,b);

Answer 1

[James Tursa]

switch choice;
    case '1'
        fprintf('What is the circle''s radius?\n')
        r = input(' ');
        [C,E] = circumference(r);
    case '2'
        fprintf('What is the ellipse''s minor and major axis lengths?\n')
        a = input('Minor length: ');
        b = input('Major length: ');
        [C,E] = circumference(a,b);
    otherwise 
        fprintf('Please enter either [1] or [2]');
end

Then write circumference to detect the number of inputs:

function c = circumference(a,b)
if( nargin == 1 )
    % use a as r
else
    % use a and b
end

[Kevin Liu]

my function file is

function [C,E] = circumference(r,a,b)

C = 2*pi*r;

E = pi*(3*(a + b) - sqrt((3*a + b)*(a + 3*b)));

whats nargin? I need both C and E tho

[James Tursa]

Your Question is setup for the user to pick either a circle or an ellipse, so why does your function above work with all three of r, a, and b? Shouldn't it be set up to use either r or a and b? Not all three in a single call. I would have expected it to be something like this:

function C = circumference(a,b) % of circle or ellipse
if( nargin == 1 ) % if the number of input arguments is 1, use circle formula
    C = 2*pi*r;
else % the number of input arguments is 2, so use ellipse formula
    C = pi*(3*(a + b) - sqrt((3*a + b)*(a + 3*b)));
end

nargin is a function that returns the number of actual input arguments that were given by the caller. There is also a function called nargout that returns the number of actual output arguments requested by the caller.