c# program structure · 2009-03-18 · 7 identifiers identifiersare the words that a programmer...
TRANSCRIPT
CSS 330 ObjectCSS 330 Object--Oriented Oriented ProgrammingProgramming
C# Program StructureC# Program Structure
2
C# Translation and ExecutionThe C# compiler translates C# source code (.csfiles) into a special representation called Microsoft Intermediate Language (MSIL)
MSIL is not the machine language for any traditional CPU, but a virtual machine
The Common Language Runtime (CLR) then interprets the MSIL file
It uses a just-in-time compiler to translate from MSIL format to machine code on the fly
3
C# Compilation and Execution
C# sourcecode
MSIL
C#compiler
Machinecode
Just in timecompiler
4
A Simple C# Program
//==========================================================// // File: HelloWorld.cs // // Classes: HelloWorld// --------------------// This program prints a string called "Hello, World!”////==========================================================
using System;
class HelloWorld{
static void Main(string[] args) {
Console.WriteLine(“Hello, World!”);}
}
5
C# Program StructureProgram specifications (optional)
//==========================================================// // File: HelloWorld.cs// // Classes: HelloWorld// --------------------// This program prints a string called "Hello, World!”////==========================================================
Library imports (optional)using System;
Class and namespace definitionsclass HelloWorld{
static void Main(string[] args) {
Console.WriteLine(“Hello, World!”);}
}
6
White Space and CommentsWhite Space
Includes spaces, newline characters, tabs, blanklinesC# programs should be formatted to enhance readability, using consistent indentation!
CommentsComments are ignored by the compiler: used only for human readers (i.e., inline documentation)
Two types of comments• Single-line comments use //…// this comment runs to the end of the line
• Multi-lines comments use /* … *//* this comment runs to the terminatingsymbol, even across line breaks */
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Identifiers
Identifiers are the words that a programmer uses in a programAn identifier can be made up of letters, digits, and the underscore characterThey cannot begin with a digitC# is case sensitive, therefore args and Args are different identifiersSometimes we choose identifiers ourselves when writing a program (such as HelloWorld)Sometimes we are using another programmer's code, so we use the identifiers that they chose (such as WriteLine)
using System;class HelloWorld{
static void Main(string[] args) {
Console.WriteLine(“Hello World!”);}
}
8
Identifiers: Keywords
Often we use special identifiers called keywords that already have a predefined meaning in the language
Example: classA keyword cannot be used in any other way
C# Keywords abstract as base bool break byte case catch char checked class const continue decimal default delegate do double else enum event explicit extern false finally fixed float for foreach get goto if implicit in int interface internal is lock long namespace new null object operator out override params private protected public readonly ref return sbyte sealed set short sizeof stackalloc static string struct switch this throw true try typeof uint ulong unchecked unsafe ushort using value virtual void volatile while
All C# keywords are lowercase!
9
NamespacesPartition the name space to avoid name conflict!All .NET library code are organized using namespaces!By default, C# code is contained in the global namespaceTo refer to code within a namespace, must use qualified name (as in System.Console) or import explicitly (as in using System; )
using System;
class HelloWorld{
static void Main(string[] args) {
Console.WriteLine(“Hello World!”);}
}
class HelloWorld{
static void Main(string[] args) {
System.Console.WriteLine(“Hello World!”);}
}
10
C# Program Structure: Method
class HelloWorld
{
}
// comments about the class
static void Main (string[] args)
{
}
// comments about the method
Console.Write(“Hello World!”);Console.WriteLine(“This is from CS112!”);
Outline
Welcome1.cs
Program Output
1 // Welcome1.cs2 // A program in C#.34 using System;56 class Welcome17 {8 static void Main( string[] args )9 {10 Console.WriteLine( "Welcome to C# Programming!" );11 }12 }
Welcome to C# Programming!
These are two single line comments. They are ignored by the compiler and are only used to aid other programmers. They use the double slash (//)
This is the using directive. It lets the compiler know that it should include the System namespace.
This is a blank line. It means nothing to the compiler and is only used to add clarity to the program.This is the beginning of the Welcome1 class definition. It starts with the classkeyword and then the name of the class.
This is the start of the Main method. It instructs the program to do what you want.
This is a statement. Console.WriteLine outputs a string.
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Console Application vs. Window Application
Console ApplicationNo visual componentOnly text input and outputRun under Command Prompt or DOS Prompt
Window ApplicationForms with many different input and output typesContains Graphical User Interfaces (GUI)GUIs make the input and output more user friendly!Message boxes
• Within the System.Windows.Forms namespace• Used to prompt or display information to the user
Outline
Welcome4.cs
Program Output
1 // Welcome4.cs2 // Printing multiple lines in a dialog Box.3 4 using System;5 using System.Windows.Forms;6 7 class Welcome48 {9 static void Main( string[] args )10 {11 MessageBox.Show( "Welcome\nto\nC#\nprogramming!" );12 }13 }
The System.Windows.Forms namespace allows the programmer to use the MessageBox class.
This will display the contents in a message box as opposed to in the console window.
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Example
static void Main(string[] args){
int total;
total = 15;System.Console.Write(“total = “);System.Console.WriteLine(total);
total = 55 + 5;System.Console.Write(“total = “);System.Console.WriteLine(total);
}
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Constants
• A constant is similar to a variable except that it holds one value for its entire existence
• The compiler will issue an error if you try to change a constant
• In C#, we use the constant modifier to declare a constantconstant int numberOfStudents = 42;
• Why constants?– give names to otherwise unclear literal values– facilitate changes to the code– prevent inadvertent errors
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C# Data Types
• There are 15 data types in C#• Eight of them represent integers:
• byte, sbyte, short, ushort, int, uint, long,ulong• Two of them represent floating point numbers
• float, double• One of them represents decimals:
• decimal• One of them represents boolean values:
• bool• One of them represents characters:
• char• One of them represents strings:
• string• One of them represents objects:
• object
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Numeric Data Types
• The difference between the various numeric types is their size, and therefore the values they can store:
Range
0 - 255-128 - 127
-32,768 - 327670 - 65537
-2,147,483,648 – 2,147,483,6470 – 4,294,967,295-9×1018 to 9×1018
0 – 1.8×1019
±1.0×10-28; ±7.9×1028 with 28-29 significant digits
±1.5×10-45; ±3.4×1038 with 7 significant digits±5.0×10-324; ±1.7×10308 with 15-16 significant digits
Question: you need a variable to represent world population. Which type do you use?
Type
bytesbyteshortushortintuintlongulong
decimal
floatdouble
Storage
8 bits8 bits16 bits16 bits32 bits32 bits64 bits64 bits
128 bits
32 bits64 bits
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Examples of Numeric Variables
int x = 1;short y = 10;float pi = 3.14f; // f denotes floatfloat f3 = 7E-02f; // 0.07double d1 = 7E-100;// use m to denote a decimaldecimal microsoftStockPrice = 28.38m;
Example: TestNumeric.cs
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Boolean
• A bool value represents a true or false condition
• A boolean can also be used to represent any two states, such as a light bulb being on or off
• The reserved words true and false are the only valid values for a boolean type
bool doAgain = true;
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Characters
• A char is a single character from the a character set• A character set is an ordered list of characters; each character is given a
unique number• C# uses the Unicode character set, a superset of ASCII
– Uses sixteen bits per character, allowing for 65,536 unique characters– It is an international character set, containing symbols and characters from
many languages– Code chart can be found at:http://www.unicode.org/charts/
• Character literals are represented in a program by delimiting with single quotes, e.g.,
'a‘ 'X‘ '7' '$‘ ',‘
char response = ‘Y’;
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Data Input
• Console.ReadLine()– Used to get a value from the user input– Example
string myString = Console.ReadLine();
• Convert from string to the correct data type– Int32.Parse()
• Used to convert a string argument to an integer• Allows math to be preformed once the string is converted• Example:
string myString = “1023”;int myInt = Int32.Parse( myString );
– Double.Parse()– Single.Parse()
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Output
• Console.WriteLine(variableName) will print the variable
• You can use the values of some variables at some positions of a string:
System.Console.WriteLine(“{0} {1}.”, iAmVar0, iAmVar1);
• You can control the output format by using the format specifiers:
float price = 2.5f;System.Console.WriteLine(“Price = {0:C}.”, price);
Price = $2.50.
For a complete list of format specifiers, seehttp://msdn.microsoft.com/library/en-us/csref/html/vclrfFormattingNumericResultsTable.asp
Example: TaxAndTotal.cs
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TaxAndTotal.cs
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Formatting Numbers
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Arithmetic Expressions
• An expression is a combination of operators and operands• Arithmetic expressions (we will see logical expressions
later) compute numeric results and make use of the arithmetic operators:
Addition + Subtraction -Multiplication *Division /Remainder %
There are no exponents
Outline
Arithmetic.cs
1 // Arithmetic.cs2 // An arithmetic program.3 4 using System;5 6 class Arithmetic7 {8 static void Main( string[] args )9 {10 string firstNumber, // first string entered by user11 secondNumber; // second string entered by user12 13 int number1, // first number to add14 number2; // second number to add15 16 // prompt for and read first number from user as string17 Console.Write( "Please enter the first integer: " );18 firstNumber = Console.ReadLine();19 20 // read second number from user as string21 Console.Write( "\nPlease enter the second integer: " );22 secondNumber = Console.ReadLine();23 24 // convert numbers from type string to type int25 number1 = Int32.Parse( firstNumber );26 number2 = Int32.Parse( secondNumber );27 28 // do operations29 int sum = number1 + number2;30 int diff = number1 - number2;31 int mul = number1 * number2;32 int div = number1 / number2;33 int mod = number1 % number2;
This is the start of class Arithmetic
Two string variables defined over two lines
The comment after the declaration is used to briefly state the variable purposeThese are two ints that are declared
over several lines and only use one semicolon. Each is separated by a coma.
Console.ReadLine is used to take the users input and place it into a variable.
This line is considered a prompt because it asks the user to input data.
Int32.Parse is used to convert the given string into an integer. It is then stored in a variable.
The operation result are stored in result variables.
Outline
Arithmetic.cs
32 // display results33 Console.WriteLine( "\n{0} + {1} = {2}.", number1, number2, sum );34 Console.WriteLine( "\n{0} – {1} = {2}.", number1, number2, diff );35 Console.WriteLine( "\n{0} * {1} = {2}.", number1, number2, mul );36 Console.WriteLine( "\n{0} / {2} = {2}.", number1, number2, div );37 Console.WriteLine( "\n{0} % {1} = {2}.", number1, number2, mod );34 35 } // end method Main36 37 } // end class Arithmetic
Putting a variable out through Console.WriteLine is done by placing the variable after the text while using a marked place to show where the variable should be placed.
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Increment and Decrement Operators
Operator Called Sample expression Explanation ++ preincrement ++a Increment a by 1, then use the new value
of a in the expression in which a resides.
++ postincrement a++ Use the current value of a in the expression in which a resides, then increment a by 1.
-- predecrement --b Decrement b by 1, then use the new value of b in the expression in which b resides.
-- postdecrement b-- Use the current value of b in the expression in which b resides, then decrement b by 1.
The increment and decrement operators.
Outline
Increment.cs
Program Output
1 // Increment.cs2 // Preincrementing and postincrementing3 4 using System;5 6 class Increment7 {8 static void Main(string[] args)9 { 10 int c;11 12 c = 5;13 Console.WriteLine( c ); // print 514 Console.WriteLine( c++ ); // print 5 then postincrement15 Console.WriteLine( c ); // print 616 17 Console.WriteLine(); // skip a line18 19 c = 5;20 Console.WriteLine( c ); // print 521 Console.WriteLine( ++c ); // preincrement then print 622 Console.WriteLine( c ); // print 623 24 } // end of method Main25 26 } // end of class Increment
556
566
Declare variable c
c is set to 5
Display c (5)
Display c (5) then add 1
Display c (6)
Display c (6)
Add 1 then display c (6)
Display c (5)
Set c equal to 5
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Operators Associativity Type () ++ --
left to right right to left
parentheses unary postfix
++ -- + - (type) right to left unary prefix
* / % left to right multiplicative
+ - left to right additive
< <= > >= left to right relational
== != left to right equality
?: right to left conditional
= += -= *= /= %= right to left assignment
Precedence and Associativity
high
low
Outline
Increment.cs
Program Output
1 // Fig. 4.14: Increment.cs2 // Preincrementing and postincrementing3 4 using System;5 6 class Increment7 {8 static void Main(string[] args)9 { 10 int c;11 12 c = 5;13 Console.WriteLine( c ); // print 514 Console.WriteLine( c++ ); // print 5 then postincrement15 Console.WriteLine( c ); // print 616 17 Console.WriteLine(); // skip a line18 19 c = 5;20 Console.WriteLine( c ); // print 521 Console.WriteLine( ++c ); // preincrement then print 622 Console.WriteLine( c ); // print 623 24 } // end of method Main25 26 } // end of class Increment
556
566
Declare variable c
c is set to 5
Display c (5)
Display c (5) then add 1
Display c (6)
Display c (6)
Add 1 then display c (6)
Display c (5)
Set c equal to 5
Outline
Comparison.cs
1 // Comparison.cs2 // Using if statements, relational operators and equality3 // operators.4 5 using System;6 7 class Comparison8 {9 static void Main( string[] args )10 {11 int number1, // first number to compare12 number2; // second number to compare13 14 // read in first number from user15 Console.Write( "Please enter first integer: " );16 number1 = Int32.Parse( Console.ReadLine() );17 18 // read in second number from user19 Console.Write( "\nPlease enter second integer: " );20 number2 = Int32.Parse( Console.ReadLine() );21 22 if ( number1 == number2 )23 Console.WriteLine( number1 + " == " + number2 );24 25 if ( number1 != number2 )26 Console.WriteLine( number1 + " != " + number2 );27 28 if ( number1 < number2 )29 Console.WriteLine( number1 + " < " + number2 );30 31 if ( number1 > number2 )32 Console.WriteLine( number1 + " > " + number2 );33
Combining these two methods eliminates the need for a temporary string variable.
If number1 is the same as number2 this line is preformed
If number1 does not equal number2 this line of code is executed.If number1 is less than number2
the program will use this lineIf number1 is greater than number2 this line will be preformed
Outline
Comparison.cs
Program Output
34 if ( number1 <= number2 )35 Console.WriteLine( number1 + " <= " + number2 );36 37 if ( number1 >= number2 )38 Console.WriteLine( number1 + " >= " + number2 );39 40 } // end method Main41 42 } // end class Comparison
Please enter first integer: 2000
Please enter second integer: 10002000 != 10002000 > 10002000 >= 1000
Please enter first integer: 1000
Please enter second integer: 20001000 != 20001000 < 20001000 <= 2000
Please enter first integer: 1000
Please enter second integer: 10001000 == 10001000 <= 10001000 >= 1000
If number1 is less than or equal to number2 then this code will be usedLastly if number1 is greater
than or equal to number2 then this code will be executed
34
Operators Associativity Type () ++ --
left to right right to left
parentheses unary postfix
++ -- + - (type) right to left unary prefix
* / % left to right multiplicative
+ - left to right additive
< <= > >= left to right relational
== != left to right equality
?: right to left conditional
= += -= *= /= %= right to left assignment
Precedence and Associativity
high
low
35
Sequential Programming Revisited
1 // Addition.cs2 // An addition program.3 4 using System;5 6 class Addition7 {8 static void Main( string[] args )9 {10 string firstNumber, // first string entered by user11 secondNumber; // second string entered by user12 13 int number1, // first number to add14 number2, // second number to add15 sum; // sum of number1 and number216 17 // prompt for and read first number from user as string18 Console.Write( "Please enter the first integer: " );19 firstNumber = Console.ReadLine();20 21 // read second number from user as string22 Console.Write( "\nPlease enter the second integer: " );23 secondNumber = Console.ReadLine();24 25 // convert numbers from type string to type int26 number1 = Int32.Parse( firstNumber );27 number2 = Int32.Parse( secondNumber );28 29 // add numbers30 sum = number1 + number2;31 32 // display results33 Console.WriteLine( "\nThe sum is {0}.", sum );34 35 } // end method Main36 37 } // end class Addition
17 // prompt for and read first number from user as string
18 Console.Write( "Please enter the first integer: " );
19 firstNumber = Console.ReadLine();
20
21 // read second number from user as string
22 Console.Write( "\nPlease enter the second integer: " );
23 secondNumber = Console.ReadLine();
24
25 // convert numbers from type string to type int
26 number1 = Int32.Parse( firstNumber );
27 number2 = Int32.Parse( secondNumber );
28
29 // add numbers
30 sum = number1 + number2;
31
32 // display results
33 Console.WriteLine( "\nThe sum is {0}.", sum );
36
C# Control Structures: Selection
T
F
if structure(single selection)
if/else structure(double selection)
TF
switch structure(multiple selections)
.
.
break
break
break
break
T
T
T
F
F
F
.
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C# Control Structures: Repetition
T
F
while structure
T
F
do/while structure F
T
for structure/foreach structure
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Ternary Conditional Operator (?:)
• Conditional Operator (e1?e2:e3)– C#’s only ternary operator– Can be used to construct expressions– Similar to an if/else structure
string result;
int numQ;
…………
result = (numQ==1) ? “Quarter” : “Quarters”;
// beginning of the next statement
Outline
Analysis.cs
1 // Analysis.cs2 // Analysis of Examination Results.3 4 using System;5 6 class Analysis7 {8 static void Main( string[] args )9 {10 int passes = 0, // number of passes11 failures = 0, // number of failures12 student = 1, // student counter13 grade; // one exam grade14 15 // process 10 students; counter-controlled loop16 while ( student <= 10 ) 17 {18 Console.Write( "Enter grade (0-100): " );19 grade = Int32.Parse( Console.ReadLine() );20 21 if ( result >= 60 )22 passes = passes + 1;23 24 else25 failures = failures + 1;26 27 student = student + 1;28 }29
A while loop that will loop 10 times
A nested if statement that determines which counter should be added to
If the grade >= 60 add one to passes
Else add one to failures
Keep track of the total number of students
Initialize both passes and failures to 0Set the student count to 1
Outline
Analysis.cs
30 // termination phase31 Console.WriteLine();32 Console.WriteLine( "Passed: " + passes );33 Console.WriteLine( "Failed: " + failures );34 35 if ( passes > 8 )36 Console.WriteLine( "Raise Tuition\n" );37 38 } // end of method Main39 40 } // end of class Analysis
Display the results to the user
If the total number of passes was greater than 8 then also tell the user to raise the tuition
Outline
ForCounter.cs
Program Output
1 // ForCounter.cs2 // Counter-controlled repetition with the for structure.3 4 using System;5 6 class ForCounter7 {8 static void Main( string[] args )9 {10 // initialization, repetition condition and incrementing11 // are all included in the for structure12 for ( int counter = 1; counter <= 5; counter++ )13 Console.WriteLine( counter );14 }15 }
12345
This is where the counter variable is initialized. It is set to 1.
The loop will continue until counter is greater than five (it will stop once it gets to six)
The counter is incremented (1 is added to it)
Note: counter can only be used in the body of the for loop!
When the loop ends the variable expires! We will discuss this issue later!
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The flexibility of the for Statement
• Each expression in the header of a for loop is optional– If the initialization is left out, no initialization is performed– If the condition is left out, it is always considered to be true, and
therefore creates an infinite loop– If the increment is left out, no increment operation is performed
• Both semi-colons are always required in the for loop header
for ( ; ; ){
// do something
}
43
Statements break and continue
• Used to alter the flow of control– The break statement
• Used to exit a loop early
– The continue statement• Used to skip the rest of the statements in a loop and restart at
the first statement in the loop
• Programs can be completed without their usage; use with caution.
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The switch Statement
break;
case: a case a action(s)true
false
.
.
.
break;
case b action(s) break;
false
false
case: z case z action(s) break;
default action(s)
true
true
case: b