How to code behaviour of GUI with two variables from user and plot four types of graph as selected from the pop up menu after clicking plot button

function varargout = FirstGUI(varargin)
% FIRSTGUI MATLAB code for FirstGUI.fig
%      FIRSTGUI, by itself, creates a new FIRSTGUI or raises the existing
%      singleton*.
%
%      H = FIRSTGUI returns the handle to a new FIRSTGUI or the handle to
%      the existing singleton*.
%
%      FIRSTGUI('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in FIRSTGUI.M with the given input arguments.
%
%      FIRSTGUI('Property','Value',...) creates a new FIRSTGUI or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before FirstGUI_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to FirstGUI_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES

% Edit the above text to modify the response to help FirstGUI

% Last Modified by GUIDE v2.5 15-Dec-2019 18:48:06

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @FirstGUI_OpeningFcn, ...
                   'gui_OutputFcn',  @FirstGUI_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT


% --- Executes just before FirstGUI is made visible.
function FirstGUI_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to FirstGUI (see VARARGIN)

% Choose default command line output for FirstGUI
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);

% UIWAIT makes FirstGUI wait for user response (see UIRESUME)
% uiwait(handles.figure1);


% --- Outputs from this function are returned to the command line.
function varargout = FirstGUI_OutputFcn(hObject, eventdata, handles) 
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;


% --- Executes on selection change in popupmenu1.
function popupmenu1_Callback(hObject, eventdata, handles)
% hObject    handle to popupmenu1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
str = get(hObject, 'String');
val = get(hObject, 'value');

switch str(val)
    case 'Sine'
        handles.currentData = handles.sine;
    case 'Cosine'
        handles.currentdata = handles.cosine;
    case 'Rectangle'
        handles.currentdata = handles.rectangle;
    case 'Triangle'
        handles.currentdata = handles.triangle;
end
guidata(hObject,handles)

% Hints: contents = cellstr(get(hObject,'String')) returns popupmenu1 contents as cell array
%        contents{get(hObject,'Value')} returns selected item from popupmenu1


% --- Executes during object creation, after setting all properties.
function popupmenu1_CreateFcn(hObject, eventdata, handles)
% hObject    handle to popupmenu1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: popupmenu controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function amplitude_Callback(hObject, eventdata, handles)
% hObject    handle to amplitude (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of amplitude as text
%        str2double(get(hObject,'String')) returns contents of amplitude as a double


% --- Executes during object creation, after setting all properties.
function amplitude_CreateFcn(hObject, eventdata, handles)
% hObject    handle to amplitude (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function frequency_Callback(hObject, eventdata, handles)
% hObject    handle to frequency (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of frequency as text
%        str2double(get(hObject,'String')) returns contents of frequency as a double


% --- Executes during object creation, after setting all properties.
function frequency_CreateFcn(hObject, eventdata, handles)
% hObject    handle to frequency (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end


% --- Executes on button press in pushbutton.
function pushbutton_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton (see GCBO)
 f = str2num(get(handles.edit1,'String'));  %geting f
 A = str2num(get(handles.edit2,'String'));  % geting A
 t = 1:100
 sine = A* sin(0.02*pi*f*t);
 cosine = A * cos(0.02*pi*f*t);
 val =double(get(handles.popupmenu1,'Value'));  %geting popupmenu value(1 or 2) 
 if val==1
 plot(sine);
 else
 plot(cosine)
 end
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

[Adam Danz]

Here's some advice on getting help in this forum

https://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer