How to increment a variable

Hello. I couldn't find a way to increment a variable in MATLAB using the ++ operator. Can you help me, please? Is there a function or an operator that I can use?

Thanks in advance.

[amit dehury]

variable=variable+1

Answer 1

[John D'Errico]

To increment a variable X, simply use

X = X+1;

MATLAB does not support the increment operator ++.

[Connor Ibach]

Yes

[Xiwen Li]

Definitely yes.

[Fernando Ortega Gallego]

It doesn't matter how difficult writing that code is. The user had a reasonable doubt regarding Matlab syntax and you decide whether you wish to solve it or not, that's all.

[John D'Errico]

And I did show how to solve it, in a very simple way.

[Jan]

Typing "a = a + 1" is difficult? What about this:

out = mat2cell(index(:)', 1, ...
         diff([find([true;diff(index(:)) > 1]); numel(index)+1])');

Let's try this in C++. :-)

[Kyle]

What if you have a value which you want to increment, like this

long_variable_name(long_index1, long_index2, long_index3) += 1;

Is the recommended syntax

long_variable_name(long_index1, long_index2, long_index3) = long_variable_name(long_index1, long_index2, long_index3) + 1;

?

[Walter Roberson]

"Is the recommended syntax"

If you are computing the indices, assign them to variables and use the variables in both places.

[Kyle]

Thanks Walter. Yes, in my example, the indices are integer variables with the names "long_index{1,2,3}". Is this what you're describing? The code is good as-is?

[Walter Roberson]

Yes, that is fine. MATLAB will not need to recalculate anything in that case, only pull the indices out of memory, which is as efficient as MATLAB gets in most circumstances.

The only more efficient you could get would be for the case where you are certain that long_variable_name does not share contents with any other variable, in which case with some work it is possible to modify the variable "in-place"

[Jhonler]

Can I use 'i++;'? like in c++.

[Jan]

No, you can't do this in Matlab.

[John D'Errico]

@Jhonler you can try, but since it is not legal MATLAB syntax, it won't work. If all languages used exactly the same syntax and code, then we would only use one language.

Answer 2

[Wayne King]

How about just

a = a+1;

 a = 1;
 x = zeros(10,1);
 for k = 1:10;
   x(a)= k^2;
   a = a+1;
 end

Of course, you would never write a loop for the above, or write the loop like that even if you did, but hopefully you get the point.

[Nivethana Narayanan]

a = a+1 doesnt work as MATLAB complains that a is Unrecognized function or variable 'a'. is there a way to address this?

[Luke Simonson]

You need to initialize a as a variable before you set a = a+1.

a = 0;
a = a+1;

Answer 3

[Walter Roberson]

You could create a class with preincrement and postincrement methods.

[KHADIJA]

thanks for answering,but am just a biginer and i don t know much about matlab, could you please explian this method to me in a simple way

[Walter Roberson]

MATLAB classes are not simple. A beginner should just use a = a + 1

[Jan]

And for advanced programmers, a=a+1 is a good choice also.

[Francois Deneuville]

I just made a Class to make the i++ (or the ++i ? - i am not a C expert) functionnality happenning in Matlab.

You can try this one out.

François

classdef Ipp < handle
% Simulate in Matlab the i++ functionality 
%
% Example 1:
%    i = Ipp
%    i.p % => 1
%    i.p % => 2
%    i.p % => 3
%    i.i % => 3
%    i.i % => 3
%    
% Example 2:
%    i = Ipp(5)
%    i.p % => 6
%    i.p % => 7
%    cos(pi/8 * i.p) % => -1 
%    i.i % => 8

    properties (SetAccess = private, GetAccess = public)
        i = [];
    end
    methods
        
        function self = Ipp(varargin)     %  Constructor
            p = inputParser;
            addOptional(p, 'ini', 0, @isnumeric);
            parse(p, varargin{:});
            
            self.i = p.Results.ini;
        end
        
        function out = p(self)
            self.i =self.i + 1;
            out = self.i;
        end
        
    end
end

[Walter Roberson]

However, you cannot do any further arithmetic on the object, such as comparing the value to a bound: you can only get the value of the variable immediately after incrementing it.

[Francois Deneuville]

I think you can if you type i.i

then you get the current value

I just mofified the comments to make this more clear

[Francois Deneuville]

By the way, Walter, thanks for you comment:

You could create a class with preincrement and postincrement methods.

it was a great idea

[Jesús Ramos]

What you implemented is the ++i operator of C (or java), where the variable is increased before returning the value, if you want to implement the i++ operator, you would have to add another method to the class:

function out = post_add(self)
    temp=self.i;
    self.i=self.i+1;
    out=temp;
end