[Year 12 SofDev] C# Cheat Sheet v3.5
Phillip Donald
milsendonaldp at gmail.com
Tue Apr 23 00:24:44 UTC 2019
Some school emails don't like html files, so attached is a .txt version.
Simply download and rename to .html, if you're scared you can open up in
notepad and note that it's all just plain html and css.
On Tue, Apr 23, 2019 at 10:12 AM Cooper, Michael J <
cooper.michael.j at edumail.vic.gov.au> wrote:
> Very nice Phillip, thank you!
>
>
>
> Michael Cooper
>
> ICT Coordinator & Network Support
>
>
>
> [image: BSC Logo]
>
> braybrooksc.vic.edu.au
>
>
>
> *From:* sofdev <sofdev-bounces at edulists.com.au> *On Behalf Of *Phillip
> Donald
> *Sent:* Tuesday, 23 April 2019 9:57 AM
> *To:* Year 12 Software Development Teachers' Mailing List <
> sofdev at edulists.com.au>
> *Subject:* [Year 12 SofDev] C# Cheat Sheet v3.5
>
>
>
> Attached should be a programming resource you can use if you are using C#.
> It's a bunch of examples of common things you need to do in programming
> (but often forget exactly how, especially if you are a sleepy student).
> This resource I developed saves me so much time as a teacher telling
> students how to safely get a number (or whatever simple thing) from the
> user over and over again.
>
>
>
> Open in any good modern browser. Let me know if you think I have missed
> anything.
>
>
>
> If you port this over to your programming language maybe you could share
> it too!
> IMPORTANT - This email and any attachments may be confidential. If
> received in error, please contact us and delete all copies. Before opening
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<script src="js/scripts.js"></script>
<!-- Navigation -->
<ul>
<li><a class="active" href="#home">Home</a></li>
<li><a href="#variablescope">Variable Scope</a></li>
<li><a href="#combinestrings">Combine strings and output to console</a></li>
<li><a href="#getstring">Get a string from the user</a></li>
<li><a href="#getint">Get an integer from the user</a></li>
<li><a href="#getdouble">Get a double from the user</a></li>
<li><a href="#compstrings">Compare strings (if statements)</a></li>
<li><a href="#compnums">Compare numbers (if statements)</a></li>
<li><a href="#simplefunction">Simple functions</a></li>
<li><a href="#forloop">For loop (counted loop)</a></li>
<li><a href="#whileloop">While loop (uncounted loop)</a></li>
<li><a href="#array">Declare/Initialise an Array</a></li>
<li><a href="#arrayvalues">Assigning Values to Array Elements</a></li>
<li><a href="#arrayaccess">Accessing Array Elements</a></li>
<li><a href="#menuexample">An example console menu</a></li>
<li><a href="#consolechecknum">Simple number validation</a></li>
<li><a href="#trycatchblock">Try/Catch Block</a></li>
<li><a href="#datetostring">Date To String (Timestamps)</a></li>
<li><a href="#filesetuppath">FILES: Setup filename</a></li>
<li><a href="#filedelete">FILES: Delete</a></li>
<li><a href="#filewrite">FILES: Write</a></li>
<li><a href="#fileread">FILES: Read</a></li>
<li><a href="#fileappend">FILES: Append</a></li>
<li><a href="#roundingdoubles">Maths: Rounding</a></li>
<li><a href="#randomnumbers">Maths: Random Numbers</a></li>
<li><a href="#guigetstring">GUI: Get a string from a textbox</a></li>
<li><a href="#guigetint">GUI: Get an integer from a textbox</a></li>
<li><a href="#guioutputstring">GUI: Output a string to a label</a></li>
<li><a href="#guiradiobuttons">GUI: Radio Buttons</a></li>
<li><a href="#guigetintvalid">GUI: Get and validate a number</a></li>
<li><a href="#guigetstrvalid">GUI: Get and validate a string</a></li>
</ul>
<a id="home"></a>
<div style="margin-left:25%;padding:1px 16px;height:1000px;">
<h2>C# Cheat Sheet</h2>
<p>Forgotten how to do something? Look it up in here!</p>
<br />
<a id="variablescope"><h3>Variable Scope</h3></a>
<p>Variables live within pairs of curly brackets like these {}</p>
<p>Outside of those brackets, they cannot be accessed, so you can reuse variable names</p>
<pre><code>
private void example()
{
int intNumA = 0;
// We can access and read/modify intNumA here
for (int i = 0; i < 10; i++)
{
// We can access intNumA here, because we are still within the original {}'s
intNumA = intNumA + 2;
i = intNumA * i;
}
}
private void anotherMethod()
{
// We cannot see intNumA in here, because it is not within that block of {}'s
}
</code></pre>
<br />
<a id="combinestrings"><h3>Combine strings and output to console</h3></a>
<pre><code>
string strOne = "My name is: ";
string strTwo = "Bob";
Console.WriteLine(strOne + strTwo);
</code></pre>
<pre><code><b>
Output:
My name is: Bob
</b></code></pre>
<br />
<a id="getstring"><h3>Get a string from the user</h3></a>
<pre><code>
Console.Write("What is your name? ");
string strName = Console.ReadLine();
Console.WriteLine("Your name is " + strName);
</code></pre>
<pre><code><b>
Output:
What is your name? <i>Bob</i>
Your name is Bob
</b></code></pre>
<br />
<a id="getint"><h3>Get an integer from the user</h3></a>
<pre><code>
Console.Write("Enter number one: ");
int <b>intSumA</b> = -999; // error value
while (!int.TryParse(Console.ReadLine(), out <b>intSumA</b>))
{
Console.Write("The value must be an integer, try again: ");
}
</code></pre>
<p>Copy and paste but change what I have highlighted in bold.</p>
<br />
<a id="getdouble"><h3>Get a double from the user</h3></a>
<pre><code>
Console.Write("Enter number one: ");
double <b>dblNumA</b> = -999; // error value
while (!double.TryParse(Console.ReadLine(), out <b>dblNumA</b>))
{
Console.Write("The value must be an integer, try again: ");
}
</code></pre>
<p>Copy and paste but change what I have highlighted in bold.</p>
<br />
<a id="compstrings"><h3>Compare strings (if statements)</h3></a>
<pre><code>
string strName = "Bob";
if (strName.Equals("Awesome"))
{
Console.WriteLine("You are awesome!!");
}
else
{
Console.WriteLine("Sorry...");
}
</code></pre>
<pre><code><b>
Output:
Sorry...
</b></code></pre>
<br />
<a id="compnums"><h3>Compare numbers (if statements)</h3></a>
<pre><code>
int intNumA = 10;
int intNumB = 11;
if (intNumA == intNumB)
{
Console.WriteLine("The numbers are the same");
}
else if (intNumA < intNumB)
{
Console.WriteLine(intNumA + " is less than " + intNumB);
}
else if (intNumA > intNumB)
{
Console.WriteLine(intNumA + " is more than " + intNumB);
}
</code></pre>
<pre><code><b>
Output:
10 is less than 11
</b></code></pre>
<br />
<a id="maths"><h3>Maths with numbers</h3></a>
<pre><code>
int intNumA = 3;
int intNumB = 4;
int intPlusResult = intNumA + intNumB;
Console.WriteLine("Result: " + intPlusResult);
int intMinusResult = intNumA - intNumB;
Console.WriteLine("Result: " + intMinusResult);
int intMultiplyResult = intNumA * intNumB;
Console.WriteLine("Result: " + intMultiplyResult);
double dblDivideResult = intNumA / intNumB;
Console.WriteLine("Result: " + dblDivideResult);
</code></pre>
<pre><code><b>
Output:
Result: 7
Result: -1
Result: 12
Result: 0.75
</b></code></pre>
<br />
<a id="simplefunction"><h3>Simple functions</h3></a>
<pre><code>
static void Main(string[] args)
{
int intSumA = 10;
int intSumB = 20;
int intTotal = CalcTwoNum(intSumA, intSumB);
Console.WriteLine("Total: " + intTotal);
}
private static int CalcTwoNum(int intSumA, int intSumB)
{
int intRetVal = intSumA + intSumB;
return intRetVal;
}
</code></pre>
<pre><code><b>
Output:
Total: 30
</b></code></pre>
<br />
<a id="forloop"><h3>For loop (counted loop)</h3></a>
<pre><code>
for (int i = 0; i < 10; i++)
{
int intTemp = i * 2;
Console.WriteLine("i = " + i + " and intTemp = " + intTemp);
}
</code></pre>
<pre><code><b>
Output:
i = 0 and intTemp = 0
i = 1 and intTemp = 2
i = 2 and intTemp = 4
i = 3 and intTemp = 6
i = 4 and intTemp = 8
i = 5 and intTemp = 10
i = 6 and intTemp = 12
i = 7 and intTemp = 14
i = 8 and intTemp = 16
i = 9 and intTemp = 18
</b></code></pre>
<br />
<a id="whileloop"><h3>While loop (uncounted loop)</h3></a>
<pre><code>
int intNum = 0;
while(intNum < 10)
{
intNum = intNum + 1;
intNum = intNum * 2;
Console.WriteLine("intNum = " + intNum);
}
</code></pre>
<pre><code><b>
Output:
intNum = 2
intNum = 6
intNum = 14
</b></code></pre>
<br />
<a id="array"><h3>How to declare/initialise an array</h3></a>
<p><b>Declaring Arrays</b></p>
<p>To declare an array in C#, use the following syntax</p>
<pre><code>
datatype[] arrayName;
</code></pre>
<p>where:</p>
<p>- <i>datatype</i> is used to specify the type of elements in the array</p>
<p>- <i>arrayName</i> specifies the name of the array</p>
<p>For example</p>
<pre><code>
double[] balance;
</code></pre>
<p><b>Initialising Arrays</b></p>
<p>Declaring an array does not initialize the array in the memory. When the array variable is initialized, you can assign values to the array.</p>
<p>Array is a reference type, so you need to use the <i>new</i> keyword to create an instance of the array. For example,</p>
<pre><code>
double[] balance = new double[10];
</code></pre>
<br />
<a id="arrayvalues"><h3>Assigning Values to Array Elements</h3></a>
<p>You can assign values to individual array elements, by using the index number like -</p>
<pre><code>
double[] balance = new double[10];
balance[0] = 4500.0;
</code></pre>
<p>You can assign values to the array at the time of declaration, as shown −</p>
<pre><code>
double[] balance = { 2340.0, 4523.69, 3421.0};
</code></pre>
<p>You can also create and initialise an array, as shown -</p>
<pre><code>
int [] marks = new int[5] { 99, 98, 92, 97, 95};
</code></pre>
<br />
<a id="arrayaccess"><h3>Accessing Array Elements</h3></a>
<p>An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array. For example,</p>
<pre><code>
double salary = balance[9];
</code></pre>
<p>The following example, demonstrates the above-mentioned concepts of declaration, assignment, and accessing arrays −</p>
<pre><code>
int[] intExampleArray = new int[10]; // intExampleArray is an array of 10 integers
// initialize elements of array intExampleArray
for (int i = 0; i < 10; i++)
{
intExampleArray[i] = i + 100;
}
// output each array element's value
for (int j = 0; j < 10; j++)
{
Console.WriteLine("Element[{0}] = {1}", j, intExampleArray[j]);
}
</code></pre>
<pre><code><b>
Output:
Element[0] = 100
Element[1] = 101
Element[2] = 102
Element[3] = 103
Element[4] = 104
Element[5] = 105
Element[6] = 106
Element[7] = 107
Element[8] = 108
Element[9] = 109
</b></code></pre>
<br />
<a id="menuexample"><h3>An example console menu</h3></a>
<pre><code>
// We will use this boolean variable to control the menu
//while booMenu is true it will keep returning to the menu
bool booMenu = true;
while(booMenu == true)
{
// Display a menu
Console.WriteLine("1) Safely get an integer from the user\n2) Loop Example\nQ) Quit");
Console.Write("Type 1, 2 or Q: ");
// Get the input from the user
string strInput = Console.ReadLine();
// This if block is the menu
if(strInput.Equals("1"))
{
ParseIntExample();
Console.WriteLine("\n");
}
else if(strInput.Equals("2"))
{
LoopExample(10);
Console.WriteLine("\n");
}
else if(strInput.Equals("Q"))
{
booMenu = false;
}
else
{
Console.WriteLine("Invalid option");
Console.WriteLine("\n");
}
}
</code></pre>
<br />
<a id="consolechecknum"><h3>Simple number validation</h3></a>
<pre><code>
bool booNumCheck = true;
int intNum = -999; // error value
while (booNumCheck == true)
{
Console.Write("Enter a number between 1 and 10: ");
while (!int.TryParse(Console.ReadLine(), out intNum))
{
Console.Write("The value must be an integer, try again: ");
}
if (intNum >= 1 && intNum <= 10)
{
// number is between 1 and 10 inclusive
booNumCheck = false;
}
else
{
// number is invalid
Console.WriteLine("Invalid input, must be between 1 and 10");
}
}
Console.WriteLine("intNum is: " + intNum);
</code></pre>
<pre><code><b>
Output:
Enter a number between 1 and 10: <b>11</b>
Invalid input, must be between 1 and 10
Enter a number between 1 and 10: <b>2</b>
intNum is: 2
</b></code></pre>
<br />
<a id="trycatchblock"><h3>Try/Catch Block</h3></a>
<pre><code>
try
{
// dangerous code here!
}
catch (Exception excpFile)
{
Console.WriteLine(excpFile.ToString());
}
</code></pre>
<br />
<a id="datetostring"><h3>Date To String (Timestamps)</h3></a>
<pre><code>
DateTime dt = DateTime.Now;
string strOut = dt.ToString("G");
Console.WriteLine(strOut);
</code></pre>
<pre><code><b>
Output (depending on time of course):
12/03/2019 9:43:22 AM
</b></code></pre>
<br />
<a id="filesetuppath"><h3>FILES: Setup filename</h3></a>
<pre><code>
string strFileName = AppDomain.CurrentDomain.BaseDirectory + "amazing.txt";
</code></pre>
<p>Substitute <i>"amazing.txt"</i> with the string of your choice. Remember to have a proper filename extension!</p>
<br />
<a id="filedelete"><h3>FILES: Delete</h3></a>
<pre><code>
using System.IO; // We need this if we are going to use files!
</code></pre>
<p>Remember you need to import System.IO !!! (above)</p>
<pre><code>
try
{
// Delete the file if it exists.
if (File.Exists(strFileName))
{
File.Delete(strFileName);
}
}
catch (Exception excpFile)
{
Console.WriteLine(excpFile.ToString());
}
</code></pre>
<br />
<a id="filewrite"><h3>FILES: Write</h3></a>
<pre><code>
using System.IO; // We need this if we are going to use files!
</code></pre>
<p>Remember you need to import System.IO !!! (above)</p>
<pre><code>
try
{
// Create the actual file
using (StreamWriter fileStr = File.CreateText(strFileName))
{
string strLineOne = "This is super amazing";
// These 2 lines write out our strings to our file!
fileStr.WriteLine(strLineOne);
}
}
catch (Exception excpFile)
{
Console.WriteLine(excpFile.ToString());
}
</code></pre>
<br />
<a id="fileread"><h3>FILES: Read</h3></a>
<pre><code>
using System.IO; // We need this if we are going to use files!
</code></pre>
<p>Remember you need to import System.IO !!! (above)</p>
<pre><code>
try
{
// This block of code is how we read from a file
using (StreamReader srFileRead = File.OpenText(strFileNameA))
{
string strTemp = "";
while ((strTemp = srFileRead.ReadLine()) != null)
{
Console.WriteLine(strTemp);
}
// Make a new line to be neat
Console.WriteLine("");
}
}
catch (Exception excpFile)
{
Console.WriteLine(excpFile.ToString());
}
</code></pre>
<br />
<a id="fileappend"><h3>FILES: Append</h3></a>
<pre><code>
using System.IO; // We need this if we are going to use files!
</code></pre>
<p>Remember you need to import System.IO !!! (above)</p>
<pre><code>
try
{
if (!File.Exists(strFileName))
{
// If the file doesn't exist, we'll make a blank one
using (StreamWriter fileStr = File.CreateText(strFileName))
{
// Writing a blank text file
string strLineOne = "";
fileStr.WriteLine(strLineOne);
}
}
// This block of code will append (add to) the file
using (StreamWriter swFile = File.AppendText(strFileName))
{
Console.WriteLine("Adding 3 lines!");
swFile.WriteLine("This");
swFile.WriteLine("is extra");
swFile.WriteLine("text");
}
}
catch(Exception excpFile)
{
Console.WriteLine(excpFile.ToString());
}
</code></pre>
<br />
<a id="roundingdoubles"><h3>Math: Rounding</h3></a>
<pre><code>
// Math.Round() demonstration
double dblExample = 3.1415926535;
// how to round to the nearest whole number
double dblOutOne = Math.Round(dblExample);
Console.WriteLine(dblOutOne);
// How to round to x decimal places (in this case 3)
double dblOutTwo = Math.Round(dblExample, 3);
Console.WriteLine(dblOutTwo);
</code></pre>
<pre><code><b>
Output:
3
3.142
</b></code></pre>
<br />
<a id="randomnumbers"><h3>Math: Random Numbers</h3></a>
<pre><code>
// Generate random numbers between 1 and 6
Random randGen = new Random();
int intMin = 1;
int intMax = 7; // the maximum is an "exclusive maximum"
// Exclusive maximum means that it never occurs in output
// Generate some random numbers and display them
Console.WriteLine(randGen.Next(intMin, intMax));
Console.WriteLine(randGen.Next(intMin, intMax));
Console.WriteLine(randGen.Next(intMin, intMax));
</code></pre>
<br />
<a id="guigetstring"><h3>GUI: Get a string from a textbox</h3></a>
<pre><code>
string strName = txtName.Text;
</code></pre>
<p>strName will be whatever the use has typed into txtName. For this exact code to work you need to have put in a textbox called txtName.</p>
<br />
<a id="guigetint"><h3>GUI: Get an integer from a textbox</h3></a>
<pre><code>
int intRetVal = -999;
bool booValid = int.TryParse(txtBaseHP.Text, out intRetVal);
// If this fails to convert properly, intRetVal will = 0 and booValid will = false
</code></pre>
<p>booValid will be true if the conversion was successful. Note that we use txtBaseHP, a textbox, you will need to change this to suit your code.</p>
<br />
<a id="guioutputstring"><h3>GUI: Output a string to a label</h3></a>
<pre><code>
lblOutput.Content = "Your name is " + strName;
</code></pre>
<p><b>Output on label: </b>Your name is Bob</p>
<br />
<a id="guiradiobuttons"><h3>GUI: Radio Buttons</h3></a>
<p>Make sure to set the "GroupName" in the properties. You can also set if one is checked by default with the "IsChecked" value.</p>
<p>This example is using a simple 2 Radiobutton setup for a Yes/No. We are outputting to a label called lblOutput.</p>
<pre><code>
if (rbYes.IsChecked == true)
{
lblOutput.Content = "Yes was selected";
}
else if (rbNo.IsChecked == true)
{
lblOutput.Content = "No was selected";
}
else
{
lblOutput.Content = "Something went very wrong";
}
</code></pre>
<p>The .IsChecked property is a boolean variable.</p>
<br />
<a id="guigetintvalid"><h3>GUI: Get and validate a number</h3></a>
<pre><code>
int intPokeLvl = -999;
bool booValid = int.TryParse(txtPokeLvl.Text, out intPokeLvl);
bool booNumInRange = true;
// With this logic, we accept the number (don't turn booNumInRange to false) if it is between 1-100 inclusive.
if(intPokeLvl <= 0 || intPokeLvl > 100)
{
booNumInRange = false;
}
if (booValid == false || booNumInRange == false)
{
lblLevelError.Content = "Must be an integer between 1-100";
}
else
{
// Your code goes here, if it gets to this part of the code, it has passed all of our validation
}
</code></pre>
<p><b>Output if not a number or outside 1-100: </b>Must be an integer between 1-100</p>
<br />
<a id="guigetstrvalid"><h3>GUI: Get and validate a string</h3></a>
<pre><code>
string strName = txtName.Text;
bool booValidName = true;
// With this logic, we only accept if the user has put in something in the textbox
if (strName.Equals(""))
{
booValidName = false;
}
if (booValidName == false)
{
lblNameError.Content = "Please enter a name";
}
else
{
// Your code goes here, if it gets to this part of the code, it has passed all of our validation
}
</code></pre>
<p><b>Output if nothing was entered in the textbox: </b>Please enter a name</p>
<br />
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