Differences between C# and C++

Dr. Catherine StringfellowDr. Stewart Carpenter

.NET Framework Class Library and Namespaces

In both C++ and C#, one can develop Console and Windows applications

Window apps in C++ use MFCs, in C# use the FCL for the .NET platform

FCL is composed of many namespaces using System.Windows.Forms;

Control Structures

if, if-else, switch similar to C++ Loops similar to C++

But there is a foreach for arrays

Math Class

Class Math is located in namespace System (unnecessary to add an assembly reference)

Using methods of static classes ClassName.MethodName( argument1, arument2, … )

Example: Math.Sqrt (900.0)

ConstantsMath.PI = 3.1415926535…

Type Promotion

Implicit Conversion Coercion of arguments to a higher type when

passed to methods or in mixed-type expressions;

Explicit Conversion Done with cast or class Convert in namespace

System Cast Example: int result = Square ( (int ) y );

Value and Reference Types

Value typesContain data of the specified typeBuilt in types (int, float, double,…)Programmer created - structs and enumerations

Reference typesContain an address Built-in (array, object and string) Programmer created – Classes, Interfaces

and Delegates

Passing Arguments by Value vs. by Reference

Value types are passed by value and reference types are passed by reference by default

To pass a value type by reference so you can modify the original variable? Use the ref keyword

• with variables already initialized

Use the out keyword • when the called method will initialize it

Declaring Arrays

int[] x; // declare reference to an arrayx = new int[10]; // dynamically allocate array

Must use new operator to allocate dynamically the number of elements in the array

Array Methods and Properties

Since sorting data is important in many applications, .NET Framework includes high-speed sorting capabilities

// sort elements in array aArray.Sort( x );

// Determine number of elements in x by propertyx.Length

Multiple-Subscripted Arrays

Rectangular arrays – syntax a little different from C++

Jagged ArraysAn array of arrays of different lengths

// declaration of rectangular array

int[,] array1 = new int[5,10];

// declaration and initialization of jagged array

int [][] array2 = new int[ 3 ][];

array2[ 0 ] = new int[] { 1, 2 };

array2[ 1 ] = new int[] { 3 };

array2[ 2 ] = new int[] { 4, 5, 6 };

foreach Repetition Structure

The foreach repetition structure is used to iterate through values in arrays

No counter A variable is used to represent the value

of each element

foreach ( int grade in gradeArray ){ if ( grade < lowGrade ) lowGrade = grade;}

Initializing Class Objects: Constructors

If the constructor does not explicitly initialize data members, the data members are initialized by default Primitive numeric types are set to 0 Boolean types are set to false Reference types are set to null

Properties

Public properties allow clients to:Get (obtain the values of) private data

• and may control formatting and display

Set (assign values to) private data• and may scrutinize attempts to modify value

class Time

{

private int hour;

// property Hour

public int Hour

{

get

{ return hour; }

set

{ hour = ( ( value >= 0 && value < 24 ) ? value : 0 ); }

}

}

Use it in caller as cout << time.Hour; or time.Hour = 5;

Garbage Collection

When objects are no longer referenced, the CLR performs garbage collection

Use finalizers in conjunction with the garbage collector to release resources (database connections, file access, etc.) explicitly

Everyone in C#.NET community uses ToString to obtain an object’s string representation.

//Method of class Point to return string representation of Pointpublic override string ToString ( ){ return “(" + x + ", " + y + “)";}

// call method to display new point valuestring output += "\n\nThe new location of point is " + point;

ToString

Other “interesting” variations from familiar C++ constructs

abstract classes use keyword abstract sealed classes that cannot be overridden Interfaces use inheritance notation Delegates provide mechanism for passing

method references Exception handling includes a finally block

to release resources