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 NewCalculator
{
    public partial class MainWindow : Window
    {
        static int[] numbersArray = new int[10];
        static string[] operatorsArray = new string[9];

        static string storageVariable;
        static int numbersCounter = 0;
        static int operatorsCounter = 0;
        static int total = 0;
        static bool totalled = false;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void One_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "1";
            storageVariable += "1";
        }
        private void Two_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "2";
            storageVariable += "2";
        }
        private void Three_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "3";
            storageVariable += "3";
        }
        private void Four_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "4";
            storageVariable += "4";
        }
        private void Five_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "5";
            storageVariable += "5";
        }
        private void Six_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "6";
            storageVariable += "6";
        }
        private void Seven_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "7";
            storageVariable += "7";
        }
        private void Eight_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "8";
            storageVariable += "8";
        }
        private void Nine_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "9";
            storageVariable += "9";
        }
        private void Zero_Click(object sender, RoutedEventArgs e)
        {
            if (totalled == true)
            {
                Display.Content = "";
                totalled = false;
            }
            Display.Content += "0";
            storageVariable += "0";
        }
        private void Add_Click(object sender, RoutedEventArgs e)
        {
            setNumber(storageVariable);
            setOperator("+");
            Display.Content += "+";
        }
        private void Subtract_Click(object sender, RoutedEventArgs e)
        {
            setNumber(storageVariable);
            setOperator("-");
            Display.Content += "-";
        }
        private void Multiply_Click(object sender, RoutedEventArgs e)
        {
            setNumber(storageVariable);
            setOperator("*");
            Display.Content += "x";
        }
        private void Divide_Click(object sender, RoutedEventArgs e)
        {
            setNumber(storageVariable);
            setOperator("/");
            Display.Content += "/";
        }
        private void Equal_Click(object sender, RoutedEventArgs e)
        {
            setNumber(storageVariable);
            for (int i = 0; i < operatorsCounter; i++)
            {
                if (operatorsArray[i] == "+" && i == 0)
                {
                    total = numbersArray[i] + numbersArray[i + 1];
                }
                else if (operatorsArray[i] == "+")
                {
                    total = total + numbersArray[i + 1];
                }
                else if (operatorsArray[i] == "-" && i == 0)
                {
                    total = numbersArray[i] - numbersArray[i + 1];
                }
                else if (operatorsArray[i] == "-")
                {
                    total = total - numbersArray[i + 1];
                }
                else if (operatorsArray[i] == "*" && i == 0)
                {
                    total = numbersArray[i] * numbersArray[i + 1];
                }
                else if (operatorsArray[i] == "*")
                {
                    total = total * numbersArray[i + 1];
                }
                else if (operatorsArray[i] == "/" && i == 0)
                {
                    total = numbersArray[i] / numbersArray[i + 1];
                }
                else if (operatorsArray[i] == "/")
                {
                    total = total / numbersArray[i + 1];
                }
            }
            Display.Content = total;
            numbersArray = null;
            operatorsArray = null;
            storageVariable = null;
            numbersCounter = 0;
            operatorsCounter = 0;
            total = 0;
            totalled = true;
        }
        static void setNumber(String Number)
        {
            numbersArray[numbersCounter] = Convert.ToInt16(Number);
            storageVariable = null;
            numbersCounter++;
        }
        static void setOperator(String Op)
        {
            operatorsArray[operatorsCounter] = Op;
            operatorsCounter++;
        }
        private void AC_Click(object sender, RoutedEventArgs e)
        {
            Display.Content = "";
            numbersArray = null;
            operatorsArray = null;
            storageVariable = null;
            numbersCounter = 0;
            operatorsCounter = 0;
            total = 0;
        }
    }
}

<Window x:Class="NewCalculator.MainWindow"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            Title="Calculator" Height="200" Width="195" ResizeMode="NoResize">
        <Grid>
            <Label x:Name="Display" Content="" HorizontalAlignment="Left" Height="32" Margin="10,3,0,0" VerticalAlignment="Top" Width="138" BorderThickness="1" RenderTransformOrigin="0.543,1.375" />
            <Button x:Name="One" Content="1" HorizontalAlignment="Left" Height="20" Margin="10,40,0,0" VerticalAlignment="Top" Width="20" Click="One_Click"/>
            <Button x:Name="Two" Content="2" HorizontalAlignment="Left" Height="20" Margin="40,40,0,0" VerticalAlignment="Top" Width="20" Click="Two_Click"/>
            <Button x:Name="Three" Content="3" HorizontalAlignment="Left" Height="20" Margin="70,40,0,0" VerticalAlignment="Top" Width="20" Click="Three_Click"/>
            <Button x:Name="Four" Content="4" HorizontalAlignment="Left" Height="20" Margin="10,70,0,0" VerticalAlignment="Top" Width="20" Click="Four_Click"/>
            <Button x:Name="Five" Content="5" HorizontalAlignment="Left" Height="20" Margin="40,70,0,0" VerticalAlignment="Top" Width="20" Click="Five_Click"/>
            <Button x:Name="Six" Content="6" HorizontalAlignment="Left" Height="20" Margin="70,70,0,0" VerticalAlignment="Top" Width="20" Click="Six_Click"/>
            <Button x:Name="Seven" Content="7" HorizontalAlignment="Left" Height="20" Margin="10,100,0,0" VerticalAlignment="Top" Width="20" Click="Seven_Click"/>
            <Button x:Name="Eight" Content="8" HorizontalAlignment="Left" Height="20" Margin="40,100,0,0" VerticalAlignment="Top" Width="20" Click="Eight_Click"/>
            <Button x:Name="Nine" Content="9" HorizontalAlignment="Left" Height="20" Margin="70,100,0,0" VerticalAlignment="Top" Width="20" Click="Nine_Click"/>
            <Button x:Name="Zero" Content="0" HorizontalAlignment="Left" Height="20" Margin="40,130,0,0" VerticalAlignment="Top" Width="20" Click="Zero_Click"/>
            <Button x:Name="Add" Content="+" HorizontalAlignment="Left" Height="20" Margin="100,40,0,0" VerticalAlignment="Top" Width="20" Click="Add_Click"/>
            <Button x:Name="Subtract" Content="-" HorizontalAlignment="Left" Height="20" Margin="130,40,0,0" VerticalAlignment="Top" Width="20" Click="Subtract_Click"/>
            <Button x:Name="Multiply" Content="x" HorizontalAlignment="Left" Height="20" Margin="100,70,0,0" VerticalAlignment="Top" Width="20" Click="Multiply_Click"/>
            <Button x:Name="Divide" Content="/" HorizontalAlignment="Left" Height="20" Margin="130,70,0,0" VerticalAlignment="Top" Width="20" Click="Divide_Click"/>
            <Button x:Name="Equal" Content="=" HorizontalAlignment="Left" Height="20" Margin="100,100,0,0" VerticalAlignment="Top" Width="20" Click="Equal_Click"/>
            <Button x:Name="AC" Content="AC" Height="20" Margin="130,100,17,0" VerticalAlignment="Top" Width="30" Click="AC_Click"/>
        </Grid>
    </Window>

if (totalled == true)
{
    Display.Content = "";
    totalled = false;
}
Display.Content += "1";
storageVariable += "1";

if (totalled == true)
{
    Display.Content = "";
    totalled = false;
}
Display.Content += "2";
storageVariable += "2";

private void AC_Click(object sender, RoutedEventArgs e)
{
    Display.Content = "";
    numbersArray = null;//null pointer exception on pressing any of the arithmetic buttons
    operatorsArray = null;//null pointer exception on pressing any of the arithmetic buttons
    storageVariable = null;//null pointer exception on pressing any of the numeric buttons
    numbersCounter = 0;
    operatorsCounter = 0;
    total = 0;
}

static void setNumber(String Number)
{
    numbersArray[numbersCounter] = Convert.ToInt16(Number);//no bounds check
    storageVariable = null;//possible null pointer when clicking arithmetic button
    numbersCounter++;
}
static void setOperator(String Op)
{
    operatorsArray[operatorsCounter] = Op;//no bounds check
    operatorsCounter++;
}