Printing Text

Writing to the Console

Console.WriteLine("Hello World");      // The next item printed will be on a new line

Console.Write("Hello World");          // The next item printed will be on the same line

Print Text and an Expression

The '+' operator means addition if it is surrounded by integers, but will concatenate (stick) strings and integers together when there is a string on one side.

Console.WriteLine("I have  " + (1 + 1) + " eyes.");

Will display "I have 2 eyes.". because the 1 + 1 is in brackets, addition is performed.

Console.WriteLine("I have  " + 1 + 1 + " eyes.");

Will display "I have 11 eyes."  because it will concatenate the "I have " with the first '1'.

Print Text and a Variable

string name = "John Smith";

int year = 1882;

Console.WriteLine(name + " born in " + year);

Variables

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

Variables are containers for storing data values.

In C#, there are different types of variables (defined with different keywords), for example:

• int - stores integers (whole numbers), without decimals, such as 123 or -123

• double - stores floating point numbers, with decimals, such as 19.99 or -19.99

• char - stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotes

• string - stores text, such as "Hello World". String values are surrounded by double quotes

• bool - stores values with two states: true or false

Declaring a variable

To declare a variable, you must specify a type and a name.

Syntax:

type variableName = value

Example:

int quantity = 5;

double price = 5.99;

string item = "Popsicles";

double totalPrice = price * quantity;

Console.WriteLine("Hello Goliath.  The total price is $" + totalPrice);

User Input

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

Use the following method to read input from the user:

string name = Console.ReadLine();

All input read using ReadLine() is returned as a string.  If you need a numeric type, it must be converted.

Converting Types

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

Use the Convert class to convert a string to a numeric type:

String to Integer

string input = Console.ReadLine();

int number = Convert.ToInt32(input);

// Or all at once

int number = Convert.ToInt32(Console.ReadLine());

String to Double

string input = Console.ReadLine();

double price = Convert.ToDouble(input);

// Or all at once

double price = Convert.ToDouble(Console.ReadLine());

Random Numbers

Create a Random object.  Only once at the beginning of your program. 

Random generator = new Random();

Use the generator and the Next() method to retrieve random numbers meeting specified criteria.

generator.Next();           // generates a random integer from 0 - Maximum Integer Value

generator.Next(number);     // generate a random integer from 0 to (number-1)

generator.Next(min, max);   // generate a random integer from min to (max-1)

Examples:

int number = generator.Next(100);     // a random integer from 0-99 will be generated

int number = generator.Next(10, 100); // a random integer from 10-99 will be generated

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

}

Arrays

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

Store multiple values of the same type without making multiple variables.

Declare an array before you use it:

string[] names;

You may set all values of an array once it has been declared.

names = {"Homer", "Marge", "Bart", "Lisa", "Maggie"};

If you don't know what values you are going to store in the array, you may initialize an empty array and add items later.  You must specify a size:

names = new string[5];

This array names contains no values.  They will need to be added by index.

Set the Value of an Element

specify the index of the element you want to change.

names[0] = "Mr. Burns";       // makes the first element in names "Mr. Burns"

Retrieve the Value of an Element

Console.WriteLine(names[2]);    // Prints the element at index 2

Determine How Man Elements are in an Array

Use the Length property.

Console.WriteLine(names.Length);     // Prints out the size of the array

Displaying Currency

In order to format output as currency, you can use the ToString() method to format it.  You will pass "C" as an argument to ToString() in order to format it as currency.  It will print out a '$' and then the value followed by exactly two decimal places.

double price = 1.5;

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

This will print out: The price is $1.50