Matlab Graphical User Interface (GUI) - Simple Calculator - Diamond Matlab Tutorials

[@Electronique_IndusEniso]

help plz :
Cannot find an exact (case-sensitive) match for 'String'
The closest match is: string in C:\Program
Files\MATLAB\R2016b\toolbox\matlab\strfun\@string\string.m
Error in Simple>Calculer_Callback (line 157)
set(handles.C,String,num2str(C));
Error in gui_mainfcn (line 95)
feval(varargin{:});
Error in Simple (line 42)
gui_mainfcn(gui_State, varargin{:});
Error in
matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)Simple('Calculer_Callback',hObject,eventdata,guidata(hObject))
Error while evaluating UIControl Callback