how to make a variable execute only once ?

Hello I have a viable t I want it to be 0 only for once then I need to increment it by 1 each time when I do this

t=0;
t=t+1;

it is always = 1 ; I have also used "persistent" but I got an error "The PERSISTENT declaration must be in a function " does anyone knows how to do this ?

thank you

[Geoff Hayes]

Reema - you may need to post more of your code. Or provide some context around why you want this variable to be zero some of the time but set to one at other times. Is this meant to be some kind of boolean? Given the persistent error message, I think that you are using a script (or running some code from the command line) and so you may want to use a function instead.

[Reema Alhassan]

I need to make a string every time I run the code for example the first time Reema0 then Reema1 then Reema2 and so on and yes I'm using a script

Answer 1

[Jan]

If you need a persistent variable, it is required to store the code in a function. To be exact, at least the persistent variable must be contained in a function:

function C = YourCounter
persistent CP
if isempty(CP)
  CP = 0;
end
CP = CP + 1;
C  = CP;
end

Now the counter is increased with each call:

str = sprintf('Hello %d', YourCounter)
str = sprintf('Hello %d', YourCounter)
str = sprintf('Hello %d', YourCounter)

You can reset it by:

clear YourCounter

I suggest to write the complete code as a function, because polluting the workspaces is prone to bugs and hard to maintain.

Note: As soon as you have a brute clear all anywhere in your code, the persistent variable is killed also. So stay away from clear all.

[Reema Alhassan]

Thank you Jan !!

Answer 2

[OCDER]

Or you could make a class of type handle that stores the value of t. Every time you summon the method getStr, it'll return the "ReemaN" string AND THEN update N by 1.

%Save the following code as: MakeName.m
classdef MakeName < handle
   properties (Access = public)
      t = 0;
   end
   methods
      function incr(obj)
         obj.t = obj.t + 1;
      end
      function decr(obj)
         obj.t = obj.t - 1;
      end
      function reset(obj)
         obj.t = 0;
      end
      function S = getStr(obj)
         S = sprintf('Reema%d', obj.t);
         incr(obj);
      end
   end
end

To see how to use this object called MakeName, try the following:

A = MakeName;
A.getStr  %Reema0
A.getStr  %Reema1
A.getStr  %Reema2
A.reset   %reset value of t to 0. Same as A.t = 0;
A.getStr  %Reema0
A.t = 10; %set value of t to 10.
A.getStr  %Reema10