Variables and Data Types

String - Stores sequences of characters

string name = "Bob";

Integer - Stores numbers without decimal values

int score = 15;

Double - Stores numbers with decimal values

double price = 2.99;

Boolean - Stores True or False

bool isOver = True;

Rounding Numbers

Use the Round method from the math class to round in a variety of ways.

• Official documentation:

  • • https://docs.microsoft.com/en-us/dotnet/api/system.math.round?view=netframework-4.8

• Easy to follow tutorial:

  • • https://www.geeksforgeeks.org/c-sharp-math-round-method-set-1/

double number = 12.456;

Console.WriteLine(Math.Round(number, 2)); //prints 12.46

Displaying Currency

If you wish to display currency, use string interpolation.

OR, you can call the ToString() method when you print out the number:

double price = 1.5;

Console.WriteLine(price.ToString("C");

See this link.

Numeric Conversions

We will cover two ways to convert strings to various numeric types:

Method 1: Using the Convert class

Converting to an Integer

The convert class makes it easy to convert from any data type to any other. We store integers in a type called Int32. You will have to build your own error checking into your program.

int age;

age = Convert.ToInt32(txtAge.Text); or age = Convert.ToInt32(Console.ReadLine());

This will generate an exception if txtAge.Text (or what the user types in the console) is anything other that an valid integer.

Converting to a Double

double price;

price = Convert.ToDouble(txtPrice.Text); or price = Convert.ToDouble(Console.ReadLine());

This will generate an exception if txtPrice.Text(or what the user types in the console) is anything other that an valid double.

lblOutput.Text = price + ""; //this casts a numeric variable back to a string

Method 2: Using TryParse (has error checking built in)

This method is slightly more difficult to use, but will not crash your program if it fails.

Converting to an Integer

int age;

Int32.TryParse(txtAge.Text, out age);

if TryParse fails, age will be whatever it was before, in this case its default value of zero. TryParse also returns a boolean value of True if it was successful and False if not. We can use this to handle the error.

int age;

if (Int32.TryParse(txtAge.Text, out age)){

//success code if necessary

}

else{

//error code

}

You could also use TryParse as the condition of a while loop in a console program to repeatedly ask the user to enter a valid integer.

while (!Int32.TryParse(Console.ReadLine(), out age))

//error message

Converting to a Double

double price;

Double.TryParse(txtPrice.Text, out price);

if TryParse fails, price will be whatever it was before, in this case its default value of zero. TryParse also returns a boolean value of True if it was successful and False if not. We can use this to handle the error.

double price;

if (Double.TryParse(txtPrice.Text, out price)){

//success code

}

else{

//error code

}

You could also use TryParse as the condition of a while loop in a console program to repeatedly ask the user to enter a valid double.

while (!Double.TryParse(Console.ReadLine(), out age))

//error message

Random Numbers

Step 1 - Constructing a Random object

Random generator = new Random();

If you provide an integer seed, you will generate the same list of random numbers each time you run your program! Good for testing.

Random generator = new Random(seed) ;

Step 2 - Use one of the Next methods to retrieve a random value from your generator

int num;

num = generator.Next(); //Gets a random integer from 0 to Integer.MaxValue

num = generator.Next(max); //Gets a random integer from 0 to max - 1 (max is an integer)

num = generator.Next(min, max); //Gets a random integer from min to max - 1 (min and max are integers)

double num;

num = generator.NextDouble(); //Gets a random double from 0 to 1

num = generator.NextDouble() * 5 //Gets a random double from 0-5

num = generator.NextDouble() * 4 + 1 //Gets a random double from 1-5

Lists

Here is the official documentation for Lists: https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1?view=netframework-4.8

Declaring a list:

List<type> listName = new List<type>;

List<int> numbers = new List<int>();

List<string> names = new List<string>();

List<double> prices = new List<double>();

# of elements in a list

prices.Count

Printing elements by index:

Console.WriteLine(names[0]); //Prints first element

Console.WriteLine(names[3]); //Prints fourth element

Console.WriteLine(names[Names.Count - 1]); //Prints last element

Add Elements

Add to the end of the list:

numbers.Add(55);

Insert an element at a specific index:

names.Insert(6, "Gary"); //Inserts the name "Gary" at index 6

Remove Elements

Remove by index:

numbers.RemoveAt(5); //Removes the element at index 5

Remove by value:

name.Remove("Gary"); //Removes only the first instance of 'Gary' in the list.

while(name.Remove("Gary")); //Removes ALL instances of 'Gary' in the list.

Looping Through a List

For-Loop using an index (must use if you want to change a value in the list):

for (int i = 0; i < prices.Count; i++){

prices[i] *= 0.5; //Reduces all prices by 50%

Console.WriteLine(prices[i]); //Prints new prices after 50% discount

}

Foreach loop:

foreach (int name in names){

Console.WriteLine(name); //Prints each name

}

Reading From A Text File

There are many ways to read from a file, this covers reading a file line by line.

You must have: using System.IO; at the top of your program

foreach (string line in File.ReadLines(@"filename and path", Encoding.UTF8))

{

Console.WriteLine(line);

}

See WinForms references to get a filename from OpenFileDialog

Writing to a Text File

There are many ways to write to a file, this covers reading a file line by line.

You must have: using System.IO; at the top of your program

1 - Declare a StreamWriter:

StreamWriter writer = new StreamWriter("filename.txt");

2 - Write a line(s) to the file:

writer.WriteLine(word); //You may use a loop if you have a list of items to write to the file.

3 - Once all lines have been written, close the file:

writer.Close();

See WinForms references to get a filename from SaveFileDialog

String Interpolation

Add a $ to a string literal to indicate that variables will be included using interpolation. Put variables or expressions in {} to have them substituted in:

int time = 2

string name = "Polkaroo"

Console.WriteLine($"I saw {name} {time} days ago!");

Formatting Currency

To format a numeric type to display as currency, add :C2 inside the { } where you substitute the variable, OR use ToString("C").

double price = 4.346

Console.WriteLine($"The price is {price:C2}");

//OR

Console.WriteLine($"The price is {price.ToString("C")");

If Statements

https://www.w3schools.com/cs/cs_conditions.php

The condition of an if statement must be something that the computer can evaluate to be true or false.

It can be a boolean value, a method that returns true/false, or a conditional statement.

Here are boolean operators:

Equals: ==

Not Equals: !=

Greater than: >

Greater than or Equal to: >=

Less than: <

Less than or equal to: <=

Basic If Statement

if (condition)

{

// Block of code to be run if the condition is true

}

If...Else

Add an optional else clause if you want to run code when the if condition is not true.

if (condition)

{

// Block of code to be run if the condition is true

}

else

{

// Block of code run if the condition is false

}

If...Else If...Else

Add as many else if statements to an if statement if you want one of many possible options to be run. The else is optional.

if (condition)

{

// Block of code to be run if the condition is true

}

else if (condition)

{

// Block of code to be run if the condition is true and previous if..else if were false

}

else

{

// Block of code run if the condition is false

}

Multiple Conditions

You can test more than one condition in a single if statement

And Operator - &&

Use the and '&&' operator if you need to test for more than 1 condition to be true at the same time.

if (condition1 && condition2)

{

// Block of code run if both condition1 and condition2 are true

}

Or Operator - ||

Use the or '||' operator if you need to test for at least 1 of multiple conditions to be true.

if (condition1 || condition2)

{

// Block of code run if either condition1 or condition2 is true

}

Not Operator - !

Use the not '!' operator to make a boolean value equal to its opposite.

if (!condition)

{

// Block of code run if condition is false.

}

Loops

For Loop

https://www.w3schools.com/cs/cs_for_loop.php

A for loop is used when you know how many times you want to run a block of code.

Format:

for(starting value; condition for executing block; increment)

{

// Code block to be repeated

}

Example:

This will print the values from 0 to 4

for (int i = 0; i < 5; i++)

{

Console.WriteLine(i);

}

While Loop

The while loop repeats a block of code as long as a condition is true.

while(condition)

{

// Code to be run of condition is true

}