nargin and the if statement

Question

Nicholas Salce 2016-9-22

1
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https://ww2.mathworks.cn/matlabcentral/answers/303975-nargin-and-the-if-statement

评论： Mukesh Mani 2023-7-6

Hi Im trying to understand how to use nargin but am having an issue. Hopefully someone can shed some light on. I copied this function from my text book

function z =  sqrtfun(x,y)
if (nargin==1)
   z = sqrt(x);
elseif (nargin==2)
   z = sqrt(x+y);
end

Then in another script I have put together this code to call the function

clc;
clear;
close all;
x = input('x');
y = input('y');
z = sqrtfun(x,y);
fprintf('Answer z ::: %4.2f\n', z);

The issue i'm having is that if i leave y blank no value is displayed for z. If i enter a value for x and y i get an output value for z. I don't know why this happens??

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Answer 1

Walter Roberson 2016-9-22

2
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When you leave y blank in response to an input() prompt, what you get back is an empty array, and you provide that empty array as an argument. nargin tests the number of arguments passed, not what value they are, so it knows you are passing two arguments. This leads to the calculation

sqrt(x+y)

where x is not empty but y is empty. The sum of a non-empty array and an empty array is the empty array, so the result is empty.

You should modify your code to

function z =  sqrtfun(x,y)
if (nargin==1) || isempty(y)
   z = sqrt(x);
else
   z = sqrt(x+y);
end

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Sultan Al-Hammadi 2018-11-27

what does nargin do?

Mukesh Mani 2023-7-6

nargin tests the number of arguments passed

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Answer 2

KSSV 2016-9-22

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You change the function as follows:

function z = sqrtfun(x,varargin)
if (nargin==1) 
    z = sqrt(x); 
elseif (nargin==2) 
    y = varargin{1} ;
    z = sqrt(x+y); 
end

When you enter one value i.e. x nargin = 1 then it goes to if, if you enter two values i.e x,y nargin will be 2. y will be stored in varargin and we are calling it in else statement.