Display Value in Text Box

I am trying to display the value of a in a text box.

a=trapz(cP6-cP7);
    
    str='Area Swept: %d';
    annotation('textbox',[0.3 0.5 0.3 0.3],'String',str,'FitBoxToText','on');

Answer 1

[Rik]

You need to transform your value to text using either sprintf or num2str:

a=trapz(cP6-cP7);

str=sprintf('Area Swept: %d',a);
annotation('textbox',[0.3 0.5 0.3 0.3],'String',str,'FitBoxToText','on');

[Allison Bushman]

Thank you. How would I update the value as a point moves?

[Rik]

You can store a handle to the annotation object in a variable, after which you can modifiy the properties as you need to.

%example:
a=10;
figure(1),clf(1)%clear figure (use only for debugging)

str=sprintf('Area Swept: %d',a);
h_annot=annotation(...
    'textbox',[0.3 0.5 0.3 0.3],...
    'String',str,...
    'FitBoxToText','on');

for n=1:10
    %move it around randomly
    set(h_annot,...
        'position',[0.1+rand/5 0.4+rand/5 0.3 0.3],...
        'FitBoxToText','on')
    pause(1/3)
end

If my answer solved your problem, please consider marking it as accepted answer.