matlab calc equal button

% --- Executes on button press in eqBtn.
function eqBtn_Callback(hObject, eventdata, handles)
% Get the current text from typeBox
lastText = get(handles.typeBox, 'String');

if isfield(handles, 'lastAns')
    lastText = strrep(lastText, 'lastAns', num2str(handles.lastAns));
end

if contains(lastText, 'intg(') && contains(lastText, ')')
        % Extract the portion between 'intg(' and ')'
        equationPart = extractBetween(lastText, 'intg(', ')');
        if ~isempty(equationPart)
            parts = strsplit(equationPart{1}, ',');
            eqStr = strtrim(parts{1});
            syms x;
            symbolicExpr = str2sym(eqStr);
            minx = str2double(strtrim(parts{2}));  % The lower limit
            maxx = str2double(strtrim(parts{3}));  % The upper limit
            numericIntegral = integral(matlabFunction(symbolicExpr, 'Vars', x), minx, maxx);

            integralStr = sprintf('%f', numericIntegral);
            escapedEquationPart = regexptranslate('escape', equationPart{1});
            lastText = regexprep(lastText, ['intg\(' escapedEquationPart '\)'], integralStr);
        else
            set(handles.resultBox, 'String', 'Error with integration');
            return
        end
end
if contains(lastText, 'ddx(') && contains(lastText, ')')
    % Extract the portion between 'ddx(' and ')'
    equationPart = extractBetween(lastText, 'ddx(', ')');
    if ~isempty(equationPart)
        parts = strsplit(equationPart{1}, ',');
        eqStr = strtrim(parts{1});  % The equation
        evalPoint = str2double(strtrim(parts{2}));  % The specific x-value

        syms x;
        % Compute the derivative symbolically
        symbolicExpr = str2sym(eqStr);
        derivativeExpr = diff(symbolicExpr, x);

        numericDerivative = double(subs(derivativeExpr, x, evalPoint));

        derivativeStr = sprintf('%f', numericDerivative);
        escapedEquationPart = regexptranslate('escape', equationPart{1});
        lastText = regexprep(lastText, ['ddx\(' escapedEquationPart '\)'], derivativeStr);
    else
        set(handles.resultBox, 'String', 'Error with derivative calculation');
        return
    end
end

if contains(lastText, 'logb(') && contains(lastText, ')')
        % Extract the portion between 'intg(' and ')'
        paramsPart = extractBetween(lastText, 'logb(', ')');
        if ~isempty(paramsPart)
            parts = strsplit(paramsPart{1}, ',');
            base = str2double(strtrim(parts{1}));
            value = str2double(strtrim(parts{2}));
            logRes = log(value) / log(base);

            logStr = sprintf('%f', logRes);
            escapedEquationPart = regexptranslate('escape', paramsPart{1});
            lastText = regexprep(lastText, ['logb\(' escapedEquationPart '\)'], logStr);
        else
            set(handles.resultBox, 'String', 'Error with log');
            return
        end
end
% Try to evaluate the expression
try
    handles.lastAns = eval(lastText); % Store result in handles.lastAns
    % Update the resultBox with the result of the evaluation
    set(handles.resultBox, 'String', num2str(handles.lastAns));
catch
    handles.lastAns = 0; % Reset lastAns to 0 in case of error
    set(handles.resultBox, 'String', 'Error');
end

% Update the handles structure with the modified handles
guidata(hObject, handles);