Develop Reference

Memory game doesn't open all cards upon starting

I'm making a memory game in C#. It has 10 pairs of cards, total 20. It's supposed to work like this: When pressing the Start button, the game shuffles randomly the cards and reveals all cards. After 3 seconds it flips them. Then, the player has to find all pairs.
I'm having a problem with shuffling. I wrote this code. It's being executed when I press the Start button:
foreach (String icon in icons)
{
int x1 = r.Next(1, 21);
int x2 = r.Next(1, 21);
if (!num.Contains(x1))
{
num.Add(x1);
}
else
{
do
{
x1 = r.Next(1, 21);
} while (!num.Contains(x1));
num.Add(x1);
}
if (!num.Contains(x2))
{
num.Add(x2);
}
else
{
do
{
x2 = r.Next(1, 21);
} while (!num.Contains(x2));
num.Add(x2);
}
switch (x1)
{
case 1:
pictureBox1.Image = Image.FromFile(icon);
break;
case 2:
pictureBox2.Image = Image.FromFile(icon);
break;
case 3:
pictureBox3.Image = Image.FromFile(icon);
break;
case 4:
pictureBox4.Image = Image.FromFile(icon);
break;
case 5:
pictureBox5.Image = Image.FromFile(icon);
break;
case 6:
pictureBox6.Image = Image.FromFile(icon);
break;
case 7:
pictureBox7.Image = Image.FromFile(icon);
break;
case 8:
pictureBox8.Image = Image.FromFile(icon);
break;
case 9:
pictureBox9.Image = Image.FromFile(icon);
break;
case 10:
pictureBox10.Image = Image.FromFile(icon);
break;
case 11:
pictureBox11.Image = Image.FromFile(icon);
break;
case 12:
pictureBox12.Image = Image.FromFile(icon);
break;
case 13:
pictureBox13.Image = Image.FromFile(icon);
break;
case 14:
pictureBox14.Image = Image.FromFile(icon);
break;
case 15:
pictureBox15.Image = Image.FromFile(icon);
break;
case 16:
pictureBox16.Image = Image.FromFile(icon);
break;
case 17:
pictureBox17.Image = Image.FromFile(icon);
break;
case 18:
pictureBox18.Image = Image.FromFile(icon);
break;
case 19:
pictureBox19.Image = Image.FromFile(icon);
break;
case 20:
pictureBox20.Image = Image.FromFile(icon);
break;
}
switch (x2)
{
case 1:
pictureBox1.Image = Image.FromFile(icon);
break;
case 2:
pictureBox2.Image = Image.FromFile(icon);
break;
case 3:
pictureBox3.Image = Image.FromFile(icon);
break;
case 4:
pictureBox4.Image = Image.FromFile(icon);
break;
case 5:
pictureBox5.Image = Image.FromFile(icon);
break;
case 6:
pictureBox6.Image = Image.FromFile(icon);
break;
case 7:
pictureBox7.Image = Image.FromFile(icon);
break;
case 8:
pictureBox8.Image = Image.FromFile(icon);
break;
case 9:
pictureBox9.Image = Image.FromFile(icon);
break;
case 10:
pictureBox10.Image = Image.FromFile(icon);
break;
case 11:
pictureBox11.Image = Image.FromFile(icon);
break;
case 12:
pictureBox12.Image = Image.FromFile(icon);
break;
case 13:
pictureBox13.Image = Image.FromFile(icon);
break;
case 14:
pictureBox14.Image = Image.FromFile(icon);
break;
case 15:
pictureBox15.Image = Image.FromFile(icon);
break;
case 16:
pictureBox16.Image = Image.FromFile(icon);
break;
case 17:
pictureBox17.Image = Image.FromFile(icon);
break;
case 18:
pictureBox18.Image = Image.FromFile(icon);
break;
case 19:
pictureBox19.Image = Image.FromFile(icon);
break;
case 20:
pictureBox20.Image = Image.FromFile(icon);
break;
}
There is also an auxiliary list "num" and a list "icons", which contains the names of the icons' files.
List<int> num = new List<int>();
List<String> icons = new List<String>() { "agelada.png", "elefantas.png", "gata.png", "gatopardos.png", "kamilopardali.png", "liontari.png", "lykos.png", "skylos.png", "tigris.png", "zebra.png" };
This code is supposed to work like this:
~It generates two random numbers, from 1 to 20 (the game has 20 cards), and stores them into x1 and x2 respectively.
~For each icon, member of the "icons" list: If x1 isn't found in the list num, it gets added in it. If x1 is found, a new number is being generated, until generating one that isn't in "num". Then it gets stored in "num". Same for x2. This process repeats for all the member of the list "icons".
~Then, depending of the randomly generated numbers, the icon gets inserted into the respective pictureBoxes, for example, if the numbers are 6 and 17, the picture is entered into pictureBox6 and pictureBox17.
The goal of this process is to make sure that all 10 pictures are displayed exactly twice, to make pairs.
However, I have a problem. When I click on Start, not all cards are flipped (The question mark is the "back side" of the cards). It looks like this:
Picture
It's supposed to show animal pictures in all cards.
Any ideas?

In addition to the recommendations around managing the PictureBox controls in arrays, I would recommend you change the line (not shown) where you create the Random object to something like this:
Random r = new Random(10);
Setting the seed like this while you're debugging will let you predict the output, and as you step through code from one run to the next run, it's easier to follow what's happening.
That said, if you stepped through this code:
do
{
x1 = r.Next(1, 21);
} while (!num.Contains(x1));
num.Add(x1);
If you stopped the code on adding the value to your array, you would have seen the value already exists in the array, which is the opposite of the intended action. That means your loop is exiting at the wrong time.
In this case, it's because your check is the opposite logic of what it should be, you want to keep running through this loop while the value is in the array. In other words, changing both loops to look like this:
do
{
x1 = r.Next(1, 21);
} while (num.Contains(x1));
num.Add(x1);
You will end up filling up your array with 20 unique values.

"Reset" switch statement after value is equal

I'd like to run my switch and if/else statement again after the buttons are clicked three times in total.
The current pressed code is for three buttons with each 1 value. If those (current pressed code) are equal to the global string that contains a 3 number value, the picture box color will change to forest green. This is my code:
switch ((sender as Button).Text)
{
case "1":
serialMonitor.PrintLine("1");
currentPressedCode = currentPressedCode + "1";
break;
case "2":
serialMonitor.PrintLine("2");
currentPressedCode = currentPressedCode + "2";
break;
case "3":
serialMonitor.PrintLine("3");
currentPressedCode = currentPressedCode + "3";
break;
default:
break;
} if (buttonsPressed == 3)
{
if (currentPressedCode == vaultCode)
{
//vault open
serialMonitor.PrintLine("vault");
pcbGreen.BackColor = Color.ForestGreen;
}
}
else
{
// wrong code
serialMonitor.PrintLine("wrong");
MessageBox.Show("Wrong password"); // wrong password messagebox
pcbRed.BackColor = Color.DarkRed;
}

There are many ways you could accomplish this, but trying to keep your logic intact as much as possible:
switch ((sender as Button).Text)
{
case "1":
serialMonitor.PrintLine("1");
currentPressedCode = currentPressedCode + "1";
break;
case "2":
serialMonitor.PrintLine("2");
currentPressedCode = currentPressedCode + "2";
break;
case "3":
serialMonitor.PrintLine("3");
currentPressedCode = currentPressedCode + "3";
break;
default:
break;
}
if (buttonsPressed == 3)
{
if (currentPressedCode == vaultCode)
{
//vault open
serialMonitor.PrintLine("vault");
pcbGreen.BackColor = Color.ForestGreen;
}
else
{
// wrong code
serialMonitor.PrintLine("wrong");
MessageBox.Show("Wrong password"); // wrong password messagebox
pcbRed.BackColor = Color.DarkRed;
}
buttonsPressed = 0;
currentPressedCode = "";
}
The only changes I made were:
Moving your "Wrong Password" else block after the "Right Password"
if block
Resetting buttonsPressed and the currentPressedCode
after someone has typed in 3 numbers

Xamarin studio UIImageView

I can load a picture to a UImageView with I click a button, but not from a timer. why is that ? and how can I fix it ?
here is my code :
void _timer_Elapsed(object sender, ElapsedEventArgs e)
{
Patter_Function();
switch_Function();
}
void switch_Function()
{
image1 = new UIImage();
image1 = UIImage.FromBundle("heart");
image2 = new UIImage();
image2 = UIImage.FromFile( #"White_Sharingan.png");
image3 = new UIImage();
image3 = UIImage.FromFile("snow.png");
image4 = new UIImage();
//image4.//FromFile("Images/waterfront.jpg");
switch (Patter_1[switch_Counter].Move0) {
case 0 :
Box_1.Image = image1;
break;
case 1 :
Box_1.Image = image1;
break;
case 2 :
Box_2.Image = image1;
break;
case 3:
Box_3.Image = image1;
break;
case 4:
Box_4.Image = image1;
break;
case 5:
Box_5.Image = image1;
break;
case 6:
Box_6.Image = image1;
break;
case 7:
Box_7.Image = image1;
break;
case 8:
Box12.Image = image1;
break;
case 9:
Box_9.Image = image1;
break;
case 10:
Box_10.Image = image1;
break;
case 11:
Box_11.Image = image1;
break;
case 12:
Box8.Image = image1;
break;
case 13:
Box_13.Image = image1;
break;
case 14:
Box_14.Image = image1;
break;
case 15:
Box_15.Image = image1;
break;
case 16:
Box_16.Image = image1;
break;
case 17:
Box_17.Image = image1;
break;
case 18:
Box_18.Image = image1;
break;
case 19:
Box_19.Image = image1;
break;
case 20:
Box_20.Image = image1;
break;}
switch (Patter_1[switch_Counter].Move1)
{
case 0:
Box_1.Image = image2;
break;
case 1:
Box_2.Image = image2;
break;
case 2:
Box_2.Image = image2;
break;
case 3:
Box_3.Image = image2;
break;
case 4:
Box_4.Image = image2;
break;
case 5:
Box_5.Image = image2;
break;
case 6:
Box_6.Image = image2;
break;
case 7:
Box_7.Image = image2;
break;
case 8:
Box12.Image = image2;
break;
case 9:
Box_9.Image = image2;
break;
case 10:
Box_10.Image = image2;
break;
case 11:
Box_11.Image = image2;
break;
case 12:
Box8.Image = image2;
break;
case 13:
Box_13.Image = image2;
break;
case 14:
Box_14.Image = image2;
break;
case 15:
Box_15.Image = image2;
break;
case 16:
Box_16.Image = image2;
break;
case 17:
Box_17.Image = image2;
break;
case 18:
Box_18.Image = image2;
break;
case 19:
Box_19.Image = image2;
break;
case 20:
Box_20.Image = image2;
break;
}
switch (Patter_1[switch_Counter].Move2)
{
case 0:
Box_1.Image = image3;
break;
case 1:
Box_2.Image = image3;
break;
case 2:
Box_2.Image = image3;
break;
case 3:
Box_3.Image = image3;
break;
case 4:
Box_4.Image = image3;
break;
case 5:
Box_5.Image = image3;
break;
case 6:
Box_6.Image = image3;
break;
case 7:
Box_7.Image = image3;
break;
case 8:
Box12.Image = image3;
break;
case 9:
Box_9.Image = image3;
break;
case 10:
Box_10.Image = image3;
break;
case 11:
Box_11.Image = image3;
break;
case 12:
Box8.Image = image3;
break;
case 13:
Box_13.Image = image3;
break;
case 14:
Box_14.Image = image3;
break;
case 15:
Box_15.Image = image3;
break;
case 16:
Box_16.Image = image3;
break;
case 17:
Box_17.Image = image3;
break;
case 18:
Box_18.Image = image3;
break;
case 19:
Box_19.Image = image3;
break;
case 20:
Box_20.Image = image3;
break;
}
switch (Patter_1[switch_Counter].Move3)
{
case 0:
Box_1.Image = image4;
break;
case 1:
Box_2.Image = image4;
break;
case 2:
Box_2.Image = image4;
break;
case 3:
Box_3.Image = image4;
break;
case 4:
Box_4.Image = image4;
break;
case 5:
Box_5.Image = image4;
break;
case 6:
Box_6.Image = image4;
break;
case 7:
Box_7.Image = image4;
break;
case 8:
Box12.Image = image4;
break;
case 9:
Box_9.Image = image4;
break;
case 10:
Box_10.Image = image4;
break;
case 11:
Box_11.Image = image4;
break;
case 12:
Box8.Image = image4;
break;
case 13:
Box_13.Image = image4;
break;
case 14:
Box_14.Image = image4;
break;
case 15:
Box_15.Image = image4;
break;
case 16:
Box_16.Image = image4;
break;
case 17:
Box_17.Image = image4;
break;
case 18:
Box_18.Image = image4;
break;
case 19:
Box_19.Image = image4;
break;
case 20:
Box_20.Image = image4;
break;
}
switch_Counter++;
if (switch_Counter >4 )
{
switch_Counter = 0;
}
}
I used the debugger, so I know the code is getting to the line
but it is not doing anything when it get there
the bebugger says:
UIKit.UIKitThreadAccessException: UIKit Consistency error: you are calling a UIKit method that can only be invoke from the UI Thread.
Is there a why around that ?

Any operation you involve in modifying UI view, you will need to do it under UI/Main thread. So put the code inside the lambda of:
InvokeOnMainThread ( () => {
// manipulate UI controls
});

Passing a variable from a method to a button click event

I want to be able to pass upperEncodedMsg into the text property of msgLabel at the bottom of my code.
namespace ProgrammingAssignmentDecoder
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public void Encode()
{
string message = Convert.ToString(messageTxt.Text);
char[] encodeArray = message.ToCharArray();
for (int i = 0; i < encodeArray.Length; i++)
{
char letter = (encodeArray[i]);
switch (letter)
{
case 'a':
case 'A':
encodeArray[i] = 't';
break;
case 'b':
case 'B':
encodeArray[i] = 'u';
break;
case 'c':
case 'C':
encodeArray[i] = 'v';
break;
case 'd':
case 'D':
encodeArray[i] = 'w';
break;
case 'e':
case 'E':
encodeArray[i] = 'x';
break;
case 'f':
case 'F':
encodeArray[i] = 'y';
break;
case 'g':
case 'G':
encodeArray[i] = 'z';
break;
case 'h':
case 'H':
encodeArray[i] = 'a';
break;
case 'i':
case 'I':
encodeArray[i] = 'b';
break;
case 'j':
case 'J':
encodeArray[i] = 'c';
break;
case 'k':
case 'K':
encodeArray[i] = 'd';
break;
case 'l':
case 'L':
encodeArray[i] = 'e';
break;
case 'm':
case 'M':
encodeArray[i] = 'f';
break;
case 'n':
case 'N':
encodeArray[i] = 'g';
break;
case 'o':
case 'O':
encodeArray[i] = 'h';
break;
case 'p':
case 'P':
encodeArray[i] = 'i';
break;
case 'q':
case 'Q':
encodeArray[i] = 'j';
break;
case 'r':
case 'R':
encodeArray[i] = 'k';
break;
case 's':
case 'S':
encodeArray[i] = 'l';
break;
case 't':
case 'T':
encodeArray[i] = 'm';
break;
case 'u':
case 'U':
encodeArray[i] = 'n';
break;
case 'v':
case 'V':
encodeArray[i] = 'o';
break;
case 'w':
case 'W':
encodeArray[i] = 'p';
break;
case 'x':
case 'X':
encodeArray[i] = 'q';
break;
case 'y':
case 'Y':
encodeArray[i] = 'r';
break;
case 'z':
case 'Z':
encodeArray[i] = 's';
break;
}
}
}
static string upperEncoded(char[] encodeArray, string upperEncodedMsg)
{
string encodedMsg = new string(encodeArray);
upperEncodedMsg = encodedMsg.ToUpper();
return upperEncodedMsg;
}
private void clearBtn_Click(object sender, EventArgs e)
{
messageTxt.Text = string.Empty;
msgLabel.Text = string.Empty;
processedMessageLabel.Text = "Processed Message: ";
}
private void encodeBtn_Click(object sender, EventArgs e)
{
Encode();
if (messageTxt.TextLength == 0)
{
MessageBox.Show("There is no message to Encode");
}
else
{
processedMessageLabel.Text = "Encoded Message: ";
msgLabel.Visible = true;
}
msgLabel.Text = upperEncodedMsg;
}
}
}

I tried to keep your structure in tact, there are a few things that could be done in less characters and in less complicated ways, but as you are learning the language practice is the only thing that can improve your skills :) So well done.
namespace ProgrammingAssignmentDecoder
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private string upperEncodedMsg = null;
public void Encode()
{
string message = Convert.ToString(messageTxt.Text);
char[] encodeArray = message.ToCharArray();
for (int i = 0; i < encodeArray.Length; i++)
{
char letter = (encodeArray[i]);
switch (letter)
{
case 'a':
case 'A':
encodeArray[i] = 't';
break;
case 'b':
case 'B':
encodeArray[i] = 'u';
break;
case 'c':
case 'C':
encodeArray[i] = 'v';
break;
case 'd':
case 'D':
encodeArray[i] = 'w';
break;
case 'e':
case 'E':
encodeArray[i] = 'x';
break;
case 'f':
case 'F':
encodeArray[i] = 'y';
break;
case 'g':
case 'G':
encodeArray[i] = 'z';
break;
case 'h':
case 'H':
encodeArray[i] = 'a';
break;
case 'i':
case 'I':
encodeArray[i] = 'b';
break;
case 'j':
case 'J':
encodeArray[i] = 'c';
break;
case 'k':
case 'K':
encodeArray[i] = 'd';
break;
case 'l':
case 'L':
encodeArray[i] = 'e';
break;
case 'm':
case 'M':
encodeArray[i] = 'f';
break;
case 'n':
case 'N':
encodeArray[i] = 'g';
break;
case 'o':
case 'O':
encodeArray[i] = 'h';
break;
case 'p':
case 'P':
encodeArray[i] = 'i';
break;
case 'q':
case 'Q':
encodeArray[i] = 'j';
break;
case 'r':
case 'R':
encodeArray[i] = 'k';
break;
case 's':
case 'S':
encodeArray[i] = 'l';
break;
case 't':
case 'T':
encodeArray[i] = 'm';
break;
case 'u':
case 'U':
encodeArray[i] = 'n';
break;
case 'v':
case 'V':
encodeArray[i] = 'o';
break;
case 'w':
case 'W':
encodeArray[i] = 'p';
break;
case 'x':
case 'X':
encodeArray[i] = 'q';
break;
case 'y':
case 'Y':
encodeArray[i] = 'r';
break;
case 'z':
case 'Z':
encodeArray[i] = 's';
break;
}
}
foreach (char eachChar in encodeArray) {
upperEncodedMsg += eachChar;
}
}
public void upperEncoded()
{
if (upperEncodedMsg != null)
{ upperEncodedMsg = upperEncodedMsg.ToUpper(); }
}
private void clearBtn_Click(object sender, EventArgs e)
{
messageTxt.Text = string.Empty;
msgLabel.Text = string.Empty;
processedMessageLabel.Text = "Processed Message: ";
}
private void encodeBtn_Click(object sender, EventArgs e)
{
if (messageTxt.TextLength == 0)
{
MessageBox.Show("There is no message to Encode");
}
else
{
Encode();
upperEncoded();
processedMessageLabel.Text = "Encoded Message: ";
msgLabel.Visible = true;
}
msgLabel.Text = upperEncodedMsg;
}
}
}

I'd go down the route of creating a mapping using a Dictionary<char, char>(see here for details on Dictionary) and simply lookup the key value in the dictionary for each char in encodeArray. It may also be better to use a StringBuilder rather than just a string to store your encoded message.
Create Mapping
//Add Dictionary at the top of the class along with upperEncodedMsg string.
private Dictionary<char, char> charMapping;
private StringBuilder upperEncodedMsg;
//Create mappings. Use uppercase values here and you won't need to use your 'upperEncoded' method. This bit can be done in your Form1 constructor.
public Form1()
{
InitializeComponent();
charMapping = new Dictionary<char, char>();
charMapping.Add('A', 'T');
charMapping.Add('B', 'U');
//more mappings...
}
You can then remove the big switch statement you have and replace it with the following:
public void Encode()
{
upperEncodedMsg = new StringBuilder();
string message = Convert.ToString(messageTxt.Text);
char[] encodeArray = message.ToUpper().ToCharArray();
for(int i = 0; i < encodeArray.Length; i++)
{
//Use the mappings created earlier to get the associated char.
char outputLetter;
charMapping.TryGetValue(encodeArray[i], out outputLetter);
//Append letter to your upperEncodedMsg StringBuilder.
upperEncodedMsg.Append(outputLetter);
}
}
In your button click, at the bottom you can then add:
private void encodeBtn_Click(object sender, EventArgs e)
{
//your code...
msgLabel.Text = upperEncodedMsg.ToString();
}
The main benefit of doing it this way is that your mappings can be made available in other parts of your code. It also makes it easier to maintain and your mappings are loaded as soon as the form is, rather than waiting to call your encode method. A lookup of a Dictionary is also likely to be quicker than a large switch statement.

Switch case statement

I am trying to create an application in C# that converts numbers in a text box to roman numerals in a label control and need to use a case statement. However one of my variable Roman gets the error message: Use of unassigned local variable 'Roman'.
Here is my code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace Roman_Numeral_Converter
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void btnCalc_Click(object sender, EventArgs e)
{
int Number=int.Parse(txtNum.Text); // To hold Number
string Roman; // To hold Roman Numeral
if (Number>=1 && Number <=10)
{
switch (Roman)
{
case "Number==1":
lblRoman.Text = "I";
break;
case "Number==2":
lblRoman.Text = "II";
break;
case "Number==3":
lblRoman.Text = "III";
break;
case "Number==4":
lblRoman.Text = "IV";
break;
case "Number==5":
lblRoman.Text = "V";
break;
case "Number==6":
lblRoman.Text = "VI";
break;
case "Number==7":
lblRoman.Text = "VII";
break;
case "Number==8":
lblRoman.Text = "VIII";
break;
case "Number==9":
lblRoman.Text = "IX";
break;
case "Number==10":
lblRoman.Text = "X";
break;
}
}
else
{
MessageBox.Show("Error: Invalid Input");
}
}
private void btnExit_Click(object sender, EventArgs e)
{
// Close the form.
this.Close();
}
private void btnClear_Click(object sender, EventArgs e)
{
txtNum.Text = "";
lblRoman.Text = "";
}
}
}

Your structure is a little off.
private void btnCalc_Click(object sender, EventArgs e)
{
var Number = int.Parse(txtNum.Text); // To hold Number
switch (Number)
{
case 1:
lblRoman.Text = "I";
break;
case 2:
lblRoman.Text = "II";
break;
case 3:
lblRoman.Text = "III";
break;
case 4:
lblRoman.Text = "IV";
break;
case 5:
lblRoman.Text = "V";
break;
case 6:
lblRoman.Text = "VI";
break;
case 7:
lblRoman.Text = "VII";
break;
case 8:
lblRoman.Text = "VIII";
break;
case 9:
lblRoman.Text = "IX";
break;
case 10:
lblRoman.Text = "X";
break;
default:
MessageBox.Show("Error: Invalid Input");
break;
}
}
You're using the lblRoman to hold your result, thus your Roman variable is unnecessary. Additionally, since you're interrogating every possible valid number in your switch, you can just use the default to replace your if/else structure.
I'm assuming you're doing this as an academic exercise. That being said, I would be remiss not to point to you Mosè Bottacini's solution to this problem.

This is because Roman variable is really unassigned. You should assign it before you enter the statement

try this,
when your number value like 1 so roman number is I.
private void btnCalc_Click(object sender, EventArgs e)
{
int Number = int.Parse(txtNum.Text); // To hold Number
string Roman; // To hold Roman Numeral
if (Number >= 1 && Number <= 10)
{
switch (Number)
{
case 1:
lblRoman.Text = "I";
break;
case 2:
lblRoman.Text = "II";
break;
case 3:
lblRoman.Text = "III";
break;
case 4:
lblRoman.Text = "IV";
break;
case 5:
lblRoman.Text = "V";
break;
case 6:
lblRoman.Text = "VI";
break;
case 7:
lblRoman.Text = "VII";
break;
case 8:
lblRoman.Text = "VIII";
break;
case 9:
lblRoman.Text = "IX";
break;
case 10:
lblRoman.Text = "X";
break;
}
}
else
{
MessageBox.Show("Error: Invalid Input");
}
}

Instead of switch, You can do other way using Linq which is even better.
int Number=int.Parse(txtNum.Text);
var romanList = new List<string> {"I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX", "X"};
if (Number >= 1 && Number <= 10)
lblRoman.Text = romanList.Select((r, i) => new { Roman = r, Index = i+1}).FirstOrDefault(x=> x.Index == Number).Roman;

you can replace your switch statement this way. and of course you need to assign a variable before using it.
public string GetNum(string val)
{
string res = ""; // Assign it an empty string.
var numToRom = new Dictionary<string, string>
{
{"1","I"},
{"2","II"}
//so on
};
numToRom.TryGetValue(val, out res);
return res;
}