C#: CS1 Should We Switch ? WG2.4 AUGUST 7,2003 IRA POHL  ALGOL – PL/1 – Pascal – C / C++ / Java / C#  What have we learned from CS1 choices  Neat Features of C#  C# vs. Java vs. C++ 

Family of Languages

CS1 through the years  Academic computer science in the 60’s  ALGOL 60 vs. FORTRAN  Confusion at the end of the 60’s  Pl/1, ALGOL W, BASIC, ALGOL 68  Pascal consensus

CS1: mid-80’s through present  C++ becomes a contender: very influential  Complex, but OO starts being dominant  1995: Java phenomena  2000: Java starts achieving majority status  2002: C# – why it will replace Java  (ALGOL W v Pascal – incremental change)

Copyright Ira Pohl ALGOL 60 BLOCKS,TYPE DECLARATION,RECURSION BNF, FOR, CALL BY NAME, PUBLICATION, PROCEDURAL ENCAPSULATION CS IS DOMINATED BY NUMERICAL SCIENCE CHIEF COMPETITION IS FORTRAN

Copyright Ira Pohl TROUBLESPOTS Knuth’s 1967 Trouble spots paper: begin integer a; integer procedure f(x, y); value y, x; integer y, x; a := f := x + 1; integer procedure g(x); integer x; x := g := a + 2; a := 0; outreal(1, a + f(a,g(a))/g(a)) end;

Copyright Ira Pohl OH PASCAL NEED NON NUMERICAL TYPES RECORDS PL1 ALGOL W ALGOL68 PASCAL ALGOL W V. PASCAL V. ALGOL 68 CHEAP, WIDESPREAD, INCREMENTALLY BETTER, BOOKS

Copyright Ira Pohl MODULE AND ADT 1980 PASCAL AND STEPWISE REFINEMENT WEAK LIBRARIES, NON-MODULAR SO UCSD PASCAL, MODULA2, C, ADA SHOULD WIRTH HAVE DEVELOPED PASCAL II

Copyright Ira Pohl OO AND UNIX 1985 LARGER SCALE UNIX PROJECT INFLUENCE STUDENTS WANT JOB SKILLS MAKE AND FILES SMALLTALK OO VISIBILITY INCREASES C, C++, MOULA 2 AND PASCAL, ML

Copyright Ira Pohl JAVA C++ TOO COMPLEX BUT OO NOW DOMINATES C TO PRIMITIVE SCHEME EIFFEL …. NICHE JAVA WORE{WRITE 1 RUN EVERWHERE} APPLETS WEB NO POINTERS PURE OO NEW CONSENSUS

CS1 Requirements  Modern and supports dominant methodology  Pascal: structured programming  C#, C++, Java: OOP  Multi-platform,excellent implementation books  Type safety, assertions, error messages  syntax, runtime  In Wide Use (has yet to happen for C#)

Traditional First C# Program // Hello world in C# // by Olivia Programmer using System; class Hello { public static void Main() { Console.WriteLine("Hello, world!"); } }

“The Alpha Centarians say Hello in C#!”

Make change in C++ // Change in dimes and pennies #include using namespace std; int main() { int price, change, dimes, pennies; cout > price; change = price; // how much change dimes = change / 10; // number of dimes pennies = change % 10; // number of pennies cout << "\n\nThe change is :" << dimes << " dimes "; cout << pennies << " pennies." << endl; }

MakeChange Java by Dissection import tio.*; // use the package tio class MakeChange { public static void main(String[] args) { int price, change, dimes, pennies; System.out.println("type price (0:100):"); price = Console.in.readInt(); change = price; // how much change dimes = change / 10; // number of dimes pennies = change % 10; // number of pennies System.out.print("The change is :"); System.out.print(dimes); System.out.print(" dimes "); System.out.print(pennies); System.out.print(" pennies.\n"); } }

C# by Dissection chapter 1 example using System; class MakeChange { public static void Main() { int price, change, dimes, pennies; // declarations string data; Console.WriteLine("Enter price (0:100):"); data = Console.ReadLine(); price = int.Parse(data); change = price; // how much change dimes = change / 10; // number of dimes pennies = change % 10; // number of pennies Console.Write("\n\nThe change is: " + dimes + " dimes "); Console.WriteLine(pennies + " pennies."); } }

C# version Not much difference from Java In many examples change is a matter of style and naming conventions, such as use of Main Instead of main And Console.WriteLine()

Types: Better than C++ or Java  Simple types  character, integer, floating-point types  Boolean type  Derived types  array, string: aggregates of simple types  Enum, struct (lightweight-object)  Everything derives from object!!!  Safety with initialization rule

The foreach Statement (Arrays only) for (i = 0; i < arrayName.Length; ++i) process arrayName[i]; foreach (T variableName in arrayName) process variableName; static void WriteArray(int[] a, String arrayName) { foreach (int element in a) Console.Write(element + " "); }

Iterator Logic: IEnumerable  foreach is important idea and safer construct than standard for iteration  Later, through use of interface inheritance, student can be taught to properly constructor their own collection class  Can use foreach

Call-By-Reference Improved Over Java  To modify variables passed as parameters, use call-by-reference  Designated by added keyword ref  ref used when declaring formal parameters when passing actual arguments  It is clear that ref variables are changed

Swap Program (1 of 2) class TestSwap { public static void Main() { int numOne = 1, numTwo = 2; Swap(ref numOne, ref numTwo); Console.WriteLine("numOne = " + numOne); Console.WriteLine("numTwo = " + numTwo); }

Swap Program (2 of 2) public static void Swap(ref int x, ref int y) { int temp; Console.WriteLine("x = " + x); Console.WriteLine("y = " + y); temp = x; x = y; y = temp; Console.WriteLine("x = " + x); Console.WriteLine("y = " + y); }

True Higher Dimensional Arrays  Jagged arrays as in C++ and Java  We have a[,,] arrays and appropriate methods and properties

TwoD Program class TwoD { public static void Main() { int[,] data = new int[3,5]; //row x column Console.WriteLine("No. of elements = " + data.Length); for (int i=0; i<data.GetLength(0); ++i) { Console.WriteLine("Row " + i + ": "); for (int j=0; j<data.GetLength(1); ++j) { data[i,j] = i * j; Console.Write(data[i,j] + ", "); } Console.WriteLine(); } } }

Improved Operator Overloading  Associated assignment op implicitly overloaded  Ordinary assignment cannot be overloaded  Overloaded as static methods  Unary operators take single argument of class type  Binary operators take one or both arguments of class type

System.Object  All types inherit form class System.Object including simple native types class Person { ····· public override string ToString() { return (name + ", age is " + age + ", gender is " + gender); }

Object and Un/ Boxing Example bool flag = true, answer; double x = 3.5; object any = flag; // boxing value to // reference type answer = (bool)flag // unboxing any = x; // boxing double value  When method defined for Object such as ToString( ) is called on value type, value is boxed  Works with value types as arguments to Write( ) and WriteLine( )

Property using get and set and value public class Point { public override string ToString() { return String.Format("({0}, {1})", x, y); } public double X // property for manipulating x { get { return x; } set { x = value; } } public double Y // property for manipulating y { get { return y; } set { y = value; } } private double x, y; }

Set and Get The C# language gives a standard rather than an ad hoc scheme for providing access and mutation to underlying state variables. This teaches methodology in a more straightforward way Note the style of using X (capitalized) for the hidden x (lowercase)

Java and C++ Comparisons  As in C#, Java and C++ have constructors  C++ does not have garbage collection and relies on destructors to deallocate memory using delete  In Java, classes include ToString( ), returns a string representation of class  In C#, we can implement ToString( )

Why C# Is Better Than Java  In C#, everything is an object  C# native types to be passed by reference  C# has boxing and unboxing for generic routines  C# foreach & IEnumerator for iterator  C# has true multi-dimensional arrays  C# get and set as access methods for retrieving and changing data members values  C# programmer can readily convert Java code to C#, but not vice versa

Why C# Is Better Than Java  C# get and set to access properties for retrieving and changing data members values  Keeps data hiding with consistent methodology  The C# programmer can readily convert Java code to C#, but not vice versa

Why C# Is Better Than Java  C# has enum as type and struct as lightweight object  C# programmer can use pointers but most label code unsafe  CLR and interoperable code – such as managed C++ and VB

Why C# Is Better Than C++  C++ too complex and unsafe  C++ system-dependent  C++ not Web-ready  C++ does not manage memory  C++ has pointer types

C# and Treatment of Type  Native simple types, such as int, bool, and double are value types  User-defined class types are reference type  string is a reference type  Reference types such as person call a constructor to build instances of types  Otherwise special value null : empty reference value

Final Thoughts  C# nicely improved on Java and C++  C# can be used for everything  sockets, threading, events, sql, …XML  C# by Dissection: a plug  Parallel treatment  Students probably use all 4 languages: C, C++, Java and C#