1. Chengyu Sun California State University, Los Angeles
CS4540 Special Topics in Web Development C# for Java Programmers: Language Basics
Chengyu Sun
California State University, Los Angeles

2. Create HelloWorld in Visual Studio
Project type
Directory structure, Solution, and Project
A solution may contain multiple projects
.sln and .csproj files
Solution View and Folder View

3. Using Git Source control
File  Add to Source Control
Team Explorer
Package project (for submitting homework and labs)
Commit all changes, then
git archive -o <filename>.zip HEAD

4. Naming Conventions Use PascalCase for anything public
Use camelCase for anything private or local
See more in .NET Naming Guidelines and C# Identifier Names

5. IDE Support for Coding Conventions
Use Quick Action Fix
Customize rules with a .editorconfig file
Add an .editorconfig file to a solution or project

6. The Anatomy of a Simple C# Program
Program.cs
File
using System;
namespace ConsoleApp1 {
class Program
static void Main(string[] args)
Console.WriteLine("Hello World!"); }
Import
Namespace
Class
Main method

7. Comparison with Java Namespace is similar to package
using is similar to import
There is no relation between namespace/class and directory/file
Namespace/class name does not have to match directory/file name
A file may contain multiple namespaces
A namespace may contain multiple classes

8. Variations of Main() private or public void or int
With or without arguments
Synchronous or asynchronous

9. Elements of an Imperative Programming Language
Comments
Types
Variables and Literals
Operators and expressions
Statements
Functions and methods
Classes and Objects
Packages

10. Comments Single-line comment: // Block comment: /* */
Documentation comments: ///
Similar to Javadoc comments /** */

11. About Data Types
.NET data types (i.e. CTS data types) are defined in the System namespace
Different .NET languages have additional type keywords that are mapped to the System types
See Table 1-2 in Pro C# 7

12. Common C# Types More in Table 3-4 in Pro C# 7 C# Type System Type
Description
bool
System.Boolean
True or false
byte
System.Byte
Unsigned 8-bit integer
short
System.Int16
16-bit integer
int
System.Int32
32-bit integer
long
System.Int64
64-bit integer
float
System.Single
32-bit floating-point number
double
System.Double
64-bit floating-point number
char
System.Char
16-bit Unicode character
string
System.String
A sequence of Unicode characters
More in Table 3-4 in Pro C# 7

13. About C# Types C# type keywords are all in low case
Unlike in Java where Integer and int are different types, C# types are just aliases of the System types
E.g. Int32.Parse("123") is the same as int.Parse("123")

14. Implicit Typing Using var
var a = 10; // int
var b = 2.1; // double
var c = true; // bool
The type of the variable is determined by the compiler via type inference
Once the type of a variable is inferred, it cannot be changed
Implicit typing is particularly useful with dynamically created classes

15. Values Types and Reference Types
Java has primitive types and class types
All C# types are class types, but some are value types and some are reference types (see Figure 3-3 in Pro C# 7)
Value types behave like Java primitive types
Reference types behave like Java class types

16. Value vs. Reference int a = 10; int b = a; b = 20; // a ?? class Foo {
int value = 10; }
Foo a = new Foo();
Foo b = a;
b.value = 20;
// a.value ??

17. Pass By Value vs. Pass By Reference
int a = 10;
class Foo {
int value = 10; }
Foo a = new Foo();
void change( int a ) {
a = 20; }
change(a);
// a ??
void change( Foo a ) {
a.value = 20; }
change(a);
// a.value ??

18. Nullable Types Usually a variable of a value type always has a value
We can make a value type nullable (i.e. allowing null value) by adding a ? suffix to the type, e.g. int?
Nullable and non-nullable versions of a type are two different types
Nullable types are particularly useful when dealing with relational databases

19. enum Type enum Color { Red, Green, Blue } enum Color { Red = 100,
Color color = Color.Red;
Console.WriteLine( color == 0 );
Console.WriteLine( color.ToString() == "Red" );

20. Some C# Literals bool: true, false int: 123, 10_000, 0xFF, 0b0101
double: 1.23, 2.2e5
float: 1.23f
char: 'A', '\u0041', '\t', '\n'
string: "hello"
Other: null, default

21. Interpolated String with $
string name = "John";
string greeting = $"Hello, {name}!";
Console.WriteLine(greeting);
What's inside {} is an expression

22. The Verbatim Identifier @
string path1 = "C:\test\files";
string path2 = "C:\\test\\files";
string path3
string path4 = "C:/test/files";
Also useful for creating multiline strings

23. Constant with const double radius = 10; const double pi = 3.1415;
Console.WriteLine(pi * radius * radius);

24. Operators
All Java operators, e.g. +, ++, =, ==, !=, &, &&, ?:, ., [], new, …
Null-related operators: ?, ??
Name operator: nameof
Get the simple string name of a variable, type, or member
Quite useful in ASP.NET MVC where routes match controller/method names

25. String Equality …
== and != can be used to check string equality/inequality
This is a special case for reference types
It performs a character-by-character, case-sensitive, culture-insensitive comparison
Simple case-insensitive comparison can be done by converting both strings to upper (or lower) case

26. … String Equality
More complex comparison can be done using the Equals() method in string. For example:
s1.Equals(s2, StringComparison.CurrentCulture)
s1.Equals(s2, StringComparison.CurrentCultureIgnoreCase)
s1.Equals(s2, StringComparison.Ordinal)
s1.Equals(s2, StringComparison.OrdinalIgnoreCase)

27. String Comparison >, >=, <, <= do NOT work for strings
String comparison can be done using the Compare() static method in string
For example:
Case-sensitive
comparison using
current culture
string.Compare(s1, s2)
string.Compare(s1, s2, true)
Ignore case

28. Null Coalescing Operator ??
x != null ? x : y
x ?? y
Returns the value of x if it's not null; otherwise returns y

29. Null Conditional Operator ?
x == null ? null : x.y
x?.y
x == null ? null : x[y]
x?[y]
Used when accessing an object member or an array element
Multiple null conditional operators can be chained together, e.g. a?.b?.c?.d

30. Null Conditional Example
class Person { …
Address address; }
class Address {
string street;
string city;
string state;
string zip;
// check if a person lives in LA
if( person == null )
return false;
else {
if( person.address == null)
return person.address.city == "LA"; } ??

31. Statements Selection statements: if, if-else, switch
Loop statements: for, foreach, while, do-while
They are identical to the ones in Java except for foreach and some additional capabilities of switch

32. foreach Example
Iterate through the elements in an array or a collection
string[] colors = { "Red", "Green", "Blue" };
foreach (var color in colors)
Console.WriteLine(color);

33. Array C# arrays are mostly like Java ones Declare Allocate
int[] numbers = new int[10];
for( var i=0 ; i < numbers.Length ; ++i )
numbers[i] = i+1;
string[] strings = { "a", "b", "c" };
Populate
All in one statement

34. Array Initialization Syntax
string[] a1 = { "a", "b", "c" };
string[] a2 = new string[] { "a", "b", "c" };
int l1 = { "a", "b", "c" }.Length; // Syntax Error!
int l2 = new string[] { "a", "b", "c"}.Length;
"Array Literal"

35. Multidimensional and Jagged Arrays
Multidimensional arrays
int[,] a1 = { {1,2,3}, {4,5,6} }; // a 2x3 array
Console.WriteLine( a1[0,1] );
Jagged arrays are arrays of arrays where each array may have different number of elements
int[][] a2 = { new int[]{1,2,3}, new int[]{4,5} };
Console.WriteLine( a2[0][1] );

36. Basic IO Using the Console Class
Output: Write(), WriteLine()
Input:
Read() reads one character
ReadLine() reads one line
Example: reads the name, price, and quantity of a product
Use double.Parse() and int.Parse() to convert a string to a number

37. Formatted Output Expressions Console.WriteLine(
$"There are {quantity} {product} at ${price}" );
Console.WriteLine("There are {0} {1} at ${2}",
quantity, product, price);
Placeholders with the indexes
of the arguments

38. More Formatting Use standard format strings, e.g.
$"There are {quantity} {product} at {price:c}"
"There are {0} {1} at {2:c}"
Use custom format strings, e.g.
$"There are {quantity} {product} at ${price:0.00}"
"There are {0} {1} at ${2:0.00}"
See Formatting Types in .NET

39. Readings
Pro C# 7: Chapter 2 and 3