Add project files.

Calculators.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.5.33424.131
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SimpleCalculator", "SimpleCalculator\SimpleCalculator.csproj", "{700D1536-C47F-4849-BD33-C264C318C06C}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{700D1536-C47F-4849-BD33-C264C318C06C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{700D1536-C47F-4849-BD33-C264C318C06C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{700D1536-C47F-4849-BD33-C264C318C06C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{700D1536-C47F-4849-BD33-C264C318C06C}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {7021B25D-E767-48F5-8D9B-0C58C2FAC2D6}
+	EndGlobalSection
+EndGlobal

SimpleCalculator/App.xaml

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+<Application x:Class="SimpleCalculator.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:SimpleCalculator"
+             StartupUri="MainWindow.xaml">
+    <Application.Resources>
+        <Style TargetType="Button" x:Key="NumberButton">
+            <Setter Property="FontSize" Value="32" />
+            <Setter Property="Margin" Value="5" />
+            <Setter Property="Foreground" Value="White" />
+            <Setter Property="Background" Value="#333" />
+        </Style>
+        <Style TargetType="Button" x:Key="OperatorButton">
+            <Setter Property="FontSize" Value="32" />
+            <Setter Property="Margin" Value="5" />
+            <Setter Property="Background" Value="Orange" />
+        </Style>
+        <Style TargetType="Button" x:Key="SpecialButton">
+            <Setter Property="FontSize" Value="32" />
+            <Setter Property="Margin" Value="5" />
+        </Style>
+    </Application.Resources>
+</Application>

SimpleCalculator/App.xaml.cs

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+using System;
+using System.Collections.Generic;
+using System.Configuration;
+using System.Data;
+using System.Linq;
+using System.Threading.Tasks;
+using System.Windows;
+
+namespace SimpleCalculator;
+/// <summary>
+/// Interaction logic for App.xaml
+/// </summary>
+public partial class App : Application {
+}

SimpleCalculator/AssemblyInfo.cs

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+using System.Windows;
+
+[assembly: ThemeInfo(
+    ResourceDictionaryLocation.None, //where theme specific resource dictionaries are located
+                                     //(used if a resource is not found in the page,
+                                     // or application resource dictionaries)
+    ResourceDictionaryLocation.SourceAssembly //where the generic resource dictionary is located
+                                              //(used if a resource is not found in the page,
+                                              // app, or any theme specific resource dictionaries)
+)]

SimpleCalculator/CalculatorMV.cs

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+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+
+namespace SimpleCalculator;
+
+public partial class CalculatorMV : ObservableObject {
+
+    private enum Action {
+        None,
+        Add,
+        Subtract,
+        Multiply,
+        Divide,
+    }
+
+    private double accumulator = 0;
+    private (Action, double) currentAction = (Action.None, 0);
+    private bool isDecimal = false;
+    private bool isNegative = false;
+    private bool isResult = false;
+
+
+    [ObservableProperty]
+    private string resultText = "0";
+
+
+    [RelayCommand]
+    private void numberClicked(string value) {
+        if (this.isResult) {
+            this.ResultText = "0";
+            this.isResult = false;
+            this.accumulator = double.Parse(value);
+        }
+        if (value == "0" && this.ResultText == "0")
+            return;
+        if (this.ResultText == "0")
+            this.ResultText = "";
+        else if (this.ResultText == "-0")
+            this.ResultText = "-";
+        this.ResultText += value;
+    }
+
+    [RelayCommand]
+    private void acClicked() {
+        this.accumulator = 0;
+        this.currentAction = (Action.None, 0);
+        this.isDecimal = false;
+        this.isNegative = false;
+        this.ResultText = "0";
+    }
+
+    [RelayCommand]
+    private void invertClicked() {
+        if (this.isNegative) {
+            this.isNegative = false;
+            this.ResultText = this.ResultText.Substring(1);
+        } else {
+            this.isNegative = true;
+            this.ResultText = "-" + this.ResultText;
+        }
+    }
+
+    [RelayCommand]
+    private void percentileClicked() {
+        this.accumulator = double.Parse(this.ResultText);
+        this.accumulator *= 0.01;
+        this.ResultText = this.accumulator.ToString();
+    }
+
+    [RelayCommand]
+    private void divideClicked() {
+        var value = double.Parse(this.ResultText);
+        this.currentAction = (Action.Divide, value);
+        this.accumulator = value;
+        this.isResult = true;
+    }
+
+    [RelayCommand]
+    private void multiplyClicked() {
+        var value = double.Parse(this.ResultText);
+        this.currentAction = (Action.Multiply, value);
+        this.accumulator = value;
+        this.isResult = true;
+    }
+
+    [RelayCommand]
+    private void subtractClicked() {
+        var value = double.Parse(this.ResultText);
+        this.currentAction = (Action.Subtract, value);
+        this.accumulator = value;
+        this.isResult = true;
+    }
+
+    [RelayCommand]
+    private void addClicked() {
+        var value = double.Parse(this.ResultText);
+        this.currentAction = (Action.Add, value);
+        this.accumulator = value;
+        this.isResult = true;
+    }
+
+    [RelayCommand]
+    private void equalClicked() {
+        var (action, value) = this.currentAction;
+        switch (action) {
+            case Action.None:
+                break;
+            case Action.Add:
+                this.accumulator = value + this.accumulator;
+                break;
+            case Action.Subtract:
+                this.accumulator = value - this.accumulator;
+                break;
+            case Action.Multiply:
+                this.accumulator = value * this.accumulator;
+                break;
+            case Action.Divide:
+                this.accumulator = value / this.accumulator;
+                break;
+        }
+        this.ResultText = this.accumulator.ToString();
+        this.isResult = true;
+    }
+
+    [RelayCommand]
+    private void decimalPointClicked() {
+        this.isDecimal = true;
+        this.ResultText += ",";
+    }
+
+}

SimpleCalculator/MainWindow.xaml

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+<Window x:Class="SimpleCalculator.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:vm="clr-namespace:SimpleCalculator"
+        mc:Ignorable="d"
+        Title="MainWindow" Height="600" Width="400">
+    <Window.Resources>
+        <vm:CalculatorMV x:Key="ViewModel" />
+    </Window.Resources>
+    <Grid DataContext="{StaticResource ViewModel}">
+        <Grid.RowDefinitions>
+            <RowDefinition Height="2*" />
+            <RowDefinition Height="*" />
+            <RowDefinition Height="*" />
+            <RowDefinition Height="*" />
+            <RowDefinition Height="*" />
+            <RowDefinition Height="*" />
+        </Grid.RowDefinitions>
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="*" />
+            <ColumnDefinition Width="*" />
+            <ColumnDefinition Width="*" />
+            <ColumnDefinition Width="*" />
+        </Grid.ColumnDefinitions>
+        <Label
+            Grid.Column="0"
+            Grid.Row="0"
+            Grid.ColumnSpan="4"
+            Content="{Binding ResultText}"
+            Margin="10"
+            BorderBrush="Black"
+            BorderThickness="5"
+            Background="Green"
+            FontSize="56"
+            FontFamily="Consolas"
+            VerticalContentAlignment="Center"
+            HorizontalContentAlignment="Right"
+        />
+        <Button
+            Grid.Column="0"
+            Grid.Row="1"
+            Grid.ColumnSpan="1"
+            Content="AC"
+            Style="{StaticResource SpecialButton}"
+            Command="{Binding acClickedCommand}"
+        />
+        <Button
+            Grid.Column="1"
+            Grid.Row="1"
+            Grid.ColumnSpan="1"
+            Content="±"
+            Style="{StaticResource SpecialButton}"
+            Command="{Binding invertClickedCommand}"
+        />
+        <Button
+            Grid.Column="2"
+            Grid.Row="1"
+            Grid.ColumnSpan="1"
+            Content="%"
+            Style="{StaticResource SpecialButton}"
+            Command="{Binding percentileClickedCommand}"
+        />
+
+
+        <Button
+            Grid.Column="3"
+            Grid.Row="1"
+            Grid.ColumnSpan="1"
+            Content="÷"
+            Style="{StaticResource OperatorButton}"
+            Command="{Binding divideClickedCommand}"
+        />
+        <Button
+            Grid.Column="3"
+            Grid.Row="2"
+            Grid.ColumnSpan="1"
+            Content="×"
+            Style="{StaticResource OperatorButton}"
+            Command="{Binding multiplyClickedCommand}"
+        />
+        <Button
+            Grid.Column="3"
+            Grid.Row="3"
+            Grid.ColumnSpan="1"
+            Content="-"
+            Style="{StaticResource OperatorButton}"
+            Command="{Binding subtractClickedCommand}"
+        />
+        <Button
+            Grid.Column="3"
+            Grid.Row="4"
+            Grid.ColumnSpan="1"
+            Content="+"
+            Style="{StaticResource OperatorButton}"
+            Command="{Binding addClickedCommand}"
+        />
+        <Button
+            Grid.Column="3"
+            Grid.Row="5"
+            Grid.ColumnSpan="1"
+            Content="="
+            Style="{StaticResource OperatorButton}"
+            Command="{Binding equalClickedCommand}"
+        />
+        
+
+        <Button
+            Grid.Column="0"
+            Grid.Row="2"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="7"
+            Content="7"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="1"
+            Grid.Row="2"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="8"
+            Content="8"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="2"
+            Grid.Row="2"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="9"
+            Content="9"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="0"
+            Grid.Row="3"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="4"
+            Content="4"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="1"
+            Grid.Row="3"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="5"
+            Content="5"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="2"
+            Grid.Row="3"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="6"
+            Content="6"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="0"
+            Grid.Row="4"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="1"
+            Content="1"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="1"
+            Grid.Row="4"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="2"
+            Content="2"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="2"
+            Grid.Row="4"
+            Grid.ColumnSpan="1"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="3"
+            Content="3"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="0"
+            Grid.Row="5"
+            Grid.ColumnSpan="2"
+            Command="{Binding numberClickedCommand}"
+            CommandParameter="0"
+            Content="0"
+            Style="{StaticResource NumberButton}"
+        />
+        <Button
+            Grid.Column="2"
+            Grid.Row="5"
+            Grid.ColumnSpan="1"
+            Content=","
+            Style="{StaticResource NumberButton}"
+            Command="{Binding decimalPointClickedCommand}"
+        />
+    </Grid>
+</Window>

SimpleCalculator/MainWindow.xaml.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Navigation;
+using System.Windows.Shapes;
+
+namespace SimpleCalculator;
+/// <summary>
+/// Interaction logic for MainWindow.xaml
+/// </summary>
+public partial class MainWindow : Window {
+    public MainWindow() {
+        InitializeComponent();
+    }
+}

SimpleCalculator/SimpleCalculator.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net7.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <UseWPF>true</UseWPF>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.1.0" />
+  </ItemGroup>
+
+</Project>