how to make a variable execute only once ?

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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
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
Reema Alhassan
Reema Alhassan on 12 Jun 2018
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

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Accepted Answer

Jan on 12 Jun 2018
Edited: Jan on 12 Jun 2018
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;
CP = CP + 1;
C = CP;
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.

More Answers (1)

OCDER on 12 Jun 2018
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;
function incr(obj)
obj.t = obj.t + 1;
function decr(obj)
obj.t = obj.t - 1;
function reset(obj)
obj.t = 0;
function S = getStr(obj)
S = sprintf('Reema%d', obj.t);
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

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