Using arrow keys to increment variables within a while loop

I have a GUI that is constantly plotting a graph for a set period of time. I have a variable that I want to be able to change in real time with the left and right arrow keys. I've tried looking up code, but i'm having a hard time understanding what is being said.

For example, I used the code

    h = figure; 
    set(h,'KeyPressFcn',@KeyPressCb);

    function y = KeyPressCb(~,evnt)

        fprintf('key pressed: %s\n',evnt.Key);
        global s;
        if strcmp(evnt.Key,'rightarrow')==1
        s = evnt.Key;
        elseif strcmp(evnt.Key, 'leftarrow')==1
        s = evnt.Key;
        elseif strcmp(evnt.Key,'space')==1
        s = evnt.Key;    

        end

    end

    end

in an attempt to adjust the value of theta, but can't get it to work right? Any advice would be appreciated.

Answer 1

[Walter Roberson]

if strcmp(evnt.Key, 'rightarrow')
   theta = theta + 1;
elseif strcmp(evnt.Key, 'leftarrow')
   theta = theta - 1;
end

[Zachary Rich]

I'm getting an error,

Undefined variable "evnt" or class "evnt.Key".

Answer 2

[Saeed Jahromi]

I guess you have a typo. "event" should be correct, not "evnt".

[Walter Roberson]

No, the user had posted

    function y = KeyPressCb(~,evnt)

so the correct variable name is evnt not event .