UiTable print and data stracture change questions

 Hello 

 I am new to the gui construction and how to do things so now i am stuck with a uitable. I created a table through the guide quick start but i face some problems with the data edit. I wanna do algebric calculations with the data.
I store the uitable data to a variable like this : 
         a=get(handles.table1,'data'); 
But when i try to run the rest of the .m file

    for i = 1 : size(a,1)-1
        SectionArea(i,1)=(a(i,3)+a(i+1,3))*(a(i+1,2)-a(i,2))/2;
        P(i,1)=sqrt((a(i,3)-a(i+1,3))^2+(a(i+1,2)-a(i,2))^2);
    end

i get this error

Undefined function or method 'plus' for input arguments of type 'cell'.

Error in ==> DischargeFlow_1>calculate_Callback at 184 SectionArea(i,1)=(a(i,3)+a(i+1,3))*(a(i+1,2)-a(i,2))/2;

Error in ==> gui_mainfcn at 96 feval(varargin{:});

Error in ==> DischargeFlow_1 at 42 gui_mainfcn(gui_State, varargin{:});

Error in ==> @(hObject,eventdata)DischargeFlow_1('calculate_Callback',hObject,eventdata,guidata(hObject))

??? Error while evaluating uicontrol Callback

I tried already to use the function b=cell2mat(a) but i get this error

Error using ==> cat CAT arguments dimensions are not consistent.

Error in ==> cell2mat at 84 m = cat(1,m{:});

Error in ==> DischargeFlow_1>calculate_Callback at 176 b=cell2mat(a);

Error in ==> gui_mainfcn at 96 feval(varargin{:});

Error in ==> DischargeFlow_1 at 42 gui_mainfcn(gui_State, varargin{:});

Error in ==> @(hObject,eventdata)DischargeFlow_1('calculate_Callback',hObject,eventdata,guidata(hObject))

??? Error while evaluating uicontrol Callback

I dont know what to do and i am stuck any help would be geatfull.

Also i would like to ask how to store the data of a uitable to a .txt file