How to increment a variable
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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.
采纳的回答
John D'Errico
2016-8-26
编辑：MathWorks Support Team
2019-5-22
To increment a variable X, simply use
X = X+1;
MATLAB does not support the increment operator ++.
13 个评论
Connor Ibach
2017-11-14
Yes
Xiwen Li
2017-12-29
Definitely yes.
Fernando Ortega Gallego
2017-12-30
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
2017-12-30
And I did show how to solve it, in a very simple way.
Jan
2017-12-30
out = mat2cell(index(:)', 1, ...
diff([find([true;diff(index(:)) > 1]); numel(index)+1])');
Let's try this in C++. :-)
Kyle
2018-1-21
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
2018-1-21
"Is the recommended syntax"
If you are computing the indices, assign them to variables and use the variables in both places.
Kyle
2018-1-21
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
2018-1-22
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
2022-9-14
Can I use 'i++;'? like in c++.
Jan
2022-9-14
No, you can't do this in Matlab.
John D'Errico
2022-9-14
@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.
Rev
2025-4-12
The one thing about being able to use syntax like C++ (the increment operation) is that when you want to try out ideas or concepts, Matlab makes it easier to test out sub sections of code instead of trying to compile and run it. It is helpful to be able to implement other language syntax in my experience. Matlab let's us try out code snippets and test out DSP operations with real time interface to hardware and equipment. Not to mention not having deal with the compiler.
更多回答（2 个）
Wayne King
2013-12-24
编辑：Walter Roberson
2022-1-21
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.
2 个评论
Nivethana Narayanan
2021-11-28
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
2022-1-21
You need to initialize a as a variable before you set a = a+1.
a = 0;
a = a+1;
Walter Roberson
2013-12-24
0 个投票
You could create a class with preincrement and postincrement methods.
8 个评论
KHADIJA
2014-1-1
Walter Roberson
2014-1-1
MATLAB classes are not simple. A beginner should just use a = a + 1
Jan
2014-1-1
And for advanced programmers, a=a+1 is a good choice also.
Francois Deneuville
2019-4-17
编辑：Francois Deneuville
2019-4-17
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
2019-4-17
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
2019-4-17
编辑：Francois Deneuville
2019-4-17
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
2019-4-17
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
2021-5-29
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
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