How to design a function that compute the factorial of an integer. The function outputs an error message if user enter a non negative value?

   function [ out ] = factorialeq( integer )
   out=factorial(integer);

if( ~isreal(integer) || integer < 0)
    error(message('MATLAB:factorial:NNegativeInt'))
end

This is what I have done but it doesnt work

[Guillaume]

In what way does it doesn't work?

[Ced]

Have a look at the order in which your function content is executed. Do you notice anything that does not make sense?

[Walter Roberson]

It would be more common to test before doing the factorial

[Guillaume]

Well, actually, the order does not matter, the check is redundant anyway since it's already performed by factorial. You can take out the entire if statement, or move it before the call to factorial, it won't change the end result at all.

[Maria De Silva]

But how do I get it to return a error message saying tht the number is not an integer

Answer 1

[Alberto]

I'm not sure about what do you pretend, but I think that what you want to do is to check the input:

function [ out ] = factorialeq( integer )  
if( ~isinteger(integer) || integer < 0)
    error(message('MATLAB:factorial:NNegativeInt'))
    out = [];
else
    out=factorial(integer);
end

Please give more details.

Bests, Alberto.

[Maria De Silva]

Ill just rephrase the question. Create a function that computes the factorial of an number. It must have one input and one output. When the user input a number. eg factorialeq(4) the output should give the factorial of 4 which is 24 however if the user inputs aa negative value or non-integer value. eg factorialeq(-4) or factorialeq(1.5) the function should output and error message

[Guillaume]

@alberto,

The out = [] after the error is never going to be executed, and that line is thus pointless. error aborts program execution immediately (unless it happens within a try...catch statement in which case execution jumps to the catch immediately).

Note that there also would be no point moving the out = [] before the error since if an error occurs the function will never return a value.

[Walter Roberson]

isinteger tests for integer datatype like uint8.

Hint: when does floor not change a value?

[Alberto]

@Maria

But the function Factorial actually do that, don't?

• factorial(-4)Error using factorial (line 20) N must be an array of real non-negative integers.
• factorial(1.4)Error using factorial (line 20) N must be an array of real non-negative integers.

If you want an specific message you can put it into a try catch

function [ out ] = factorialeq( integer )  
try
    out=factorial(integer);
catch
    disp('SPECIFIC MESSAGE')
    out = 0;
end

Answer 2

[Image Analyst]

Try adapting this snippet:

% Ask user for one integer number.
defaultValue = 45;
titleBar = 'Enter an integer value';
userPrompt = 'Enter the integer';
caUserInput = inputdlg(userPrompt, titleBar, 1, {num2str(defaultValue)});
if isempty(caUserInput),return,end; % Bail out if they clicked Cancel.
% Round to nearest integer in case they entered a floating point number.
integerValue = round(str2double(cell2mat(caUserInput)));
% Check for a valid integer.
if isnan(integerValue)
    % They didn't enter a number.  
    % They clicked Cancel, or entered a character, symbols, or something else not allowed.
    integerValue = defaultValue;
    message = sprintf('I said it had to be an integer.\nI will use %d and continue.', integerValue);
    uiwait(warndlg(message));
end