Transcript
Deccansoft Software Services
Language Basics
Chapter-3
Agenda 1.
Primitive Data Types and Variable Declaration
2.
Handling Overflow Checks
3.
Casting between other data types
4.
Boxing & Unboxing
5.
Enum and Constant
6.
Operators
7.
Control Statements
8.
Working with Arrays
9.
Working with Methods
Table Of Contents P RIMITIVE D ATA T YPES AND V ARIABLE D ECLARATION
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V ARIABLE D ECLARATION S YNTAX
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H ANDLING O VERFLOW C HECKS
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C AST ING BETWEEN OTHER DA TA TYPES
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B OXING & U NBOXING
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E NUM AND C ONSTANT
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O PERATORS
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C ONTROL S TATEMENTS
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W ORKING WITH A RRAYS
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W ORKING WITH M ETHODS
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Primitive DataTypes and Variable Declaration Integral Types: DataType
Size
. Net (CTS)
Comments
byte
1
System.Byte
0 -‐ 255 It is Unsigned
Sbyte
1
System.SByte
-‐128 to 127 – Signed
Short
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System.Int16
UShort
2
System.UInt16
Int
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System.Int32
UInt
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System.Unt32
long
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System.Int64
Ulong
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System.UInt64
Floating Types (the position of decimal point is not fixed): Float
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System.Single
Has up to 8 digits after decimal
Double
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System.Double
Has up to 16 digits after decimal
Decimal*
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System.Decimal
Has 28 digits after decimal and its fixed
* Even though the decimal datatype as decimal point it’s not floating because the number of digits after decimal are fixed i.e. 28 digits. Other DataTypes: Char
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System.Char
Uses Unicode Charset and thus supports multiple languages
string **
Systring.String
Uses Unicode Charset
bool
1
System.Boolean
True / False
object **
System.Object
Generic Datatype
**All the above data types are Value Types except String and Object, which are Reference Why Data types: Ø
Based on the data type the size of variable and the format in memory is decided
Ø
Based on the data type the compiler is going to validate the expressions making the language type safe.
Memory in an application is divided into three parts. 1.
Global Memory: Used by all global variables. These variables are allocated memory when the application begins and will remain in memory throughout the life of the application.
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Stack Memory: Used by local variables of a method. When a method is invoked a stack of memory is allocated to and the stack is cleared when the method returns
3.
Heap Memory: All dynamic memory requirements of an application are fulfilled from the heap memory. After allocating some memory from heap to a variable, once its job is completed the memory must be returned back to heap so that the same can be reused for another variable.
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The value type of variable has value where as the value of a reference type is reference to value (object) on heap.
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The value (object) of a reference type is always allocated heap memory.
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Value types are allocated memory based on the scope of the variable, If its Global Variable its allocated memory in Global Memory Area, if its Local Variable or Parameter its allocated memory on stack and if it’s a member of an object its allocated memory on Heap.
Value Types directly hold the value.
ValueType
Ex: All Basic Types, Structures & Enum
Var = Value
Reference Types hold the reference to the value on
Ref type Var
Value
HEAP. Ex: String, Object, Class, Arrays, Delegates
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Variable Declaration Syntax int a,b; int a=10, b=20; •
A local variable declared must be explicitly initialized before used in an expression otherwise gives an compilation error.
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A variable declared in a block is local to the block in which it is declared.
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A variable declared in outer block cannot be re-‐declared in the inner block.
Casting: Converting data from one form to another form. If RHS expression and LHS variable are not of same data type then casting is required. Casting can be implicit casting or explicit casting. Implicit Casting: If every possible value of RHS expression is valid for a variable on LHS variable. Explicit Casting: If an RHS expression is assigned to LHS and if there is a possibility of data loss then explicit casting is needed. Program to caste integer to byte using System; class Program { public static void Main() { int n = 256; byte b; byte b1, b2, b3; b1 = b2 = 10; //In VB it is not valid b1 = b2 + b3; //Compilation Error //if either byte, short or char variables are used in an expression they are automatically raised to the rank of int. b1 = (byte)(b2 + b3); } } Code: 3.1 C#
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Handling Overflow Checks
Code snippet for handling overflow checks unchecked //Overflow checks are not done… { b = (byte) n; Console.WriteLine(b); } checked //Overflow checks are done… { b = (byte) n; Console.WriteLine(b); } To Enable / Disable Overflow checks: Project à Properties à Compile à Scroll and Click on Advanced Compile Options à Check Integer Overflow Checks
Fig: 3.1
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Note: You cannot use the checked and unchecked keywords to control floating point (non-‐integer) arithmetic. The checked and unchecked keywords control only integer arithmetic. Floating point arithmetic never throws OverflowException. Converting float & decimal datatypes double dbl = 0.6D; //0.6 float f = 0.6F; decimal dec = 0.6M; //long to float -‐ Same as VB long lng = 10L; f = lng; //because range of long is smaller than float lng = (long) f; //float and decimal requires casting dec = 10; //Integer to decimal //f = dec; //Invalid //dec = f; //Invalid f = (float) dec; dec = (decimal) f; //“decimal” should be explicitly casted to every other type if required.
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Casting between other data types Casting between other datatypes //int to char. n = c; /*c = n; invalid */ c = (char) n; //bool – int -‐ anydatatype explicit or implicit casting is not allowed either direction //string to int s = "100"; n = (int) s; //Invalid – String cannot be casted n = int.Parse(s); //if failes throws, FormatException bool bln = int.TryParse(s, out n); //n = (int) s; //Direct casting of string to int is not allowed. //int to string s = n.ToString(); //s = (string) n //Casting of int to string is not allowed Program to Print the Char equivalent of the Ascii value read from the keyboard using System; class Program { static void Main(string[] args) { string str; str = Console.ReadLine(); int n = 100; if (int.TryParse(str, out n)) Console.WriteLine((char)n); else Console.WriteLine("Invalid number"); } } Code: 3.2 C#
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Boxing & Unboxing Boxing is the term used to describe the transformation from Value Type to reference type (Object). The runtime creates a temporary reference-‐type box for the object on the heap. UnBoxing is the term used to describe the transformation from reference type (Object) to value type. We use the term cast here, as this has to be done explicitly. object obj = n; //Boxing n = (int) obj; //Unboxing 1
When a value is boxed to an object type, the object type variable cannot be used in any mathematical operations.
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When the value of object type variable cannot be assigned to variable on LHS, an Exception of type InvalidCastException is thrown.
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Excessive usage of Object data type makes the language “Loosely Typed” and also because of frequent casting requirement while Boxing and Unboxing performance is also degraded.
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Boxing / Unboxing should be used only in situations where until runtime we don’t know the type of data we are going to deal with.
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Enum and Constant Casting between other datatypes enum WeekDay : int //WeekDay is subtype of int { Sun=1, Mon, Tues, Wed=5, Thus, Fri, Sat } Enum can be subtype of any integral type only. n = 2; //n is int WeekDay wd = WeekDay.Sat; wd = (WeekDay) n; //Explicit //n = wd; //Invalid n = (int) wd; //Explicit -‐ In VB.NET it’s not required //Constant Declaration const double PI = 3.14;
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Operators Arithmetic
+, -‐, * , / , % (mod) (Power operator is missing)
Logical Operators
^ (XOR), !(NOT) && (VB-‐AndAlso) , || (VB-‐OrElse)
Ternary Operator
?:
String concatenation
+ (VB-‐&)
Increment, decrement
++ , -‐-‐
Bitwise
<< , >>, & , | , ~ (complement/negation)
Relational
= = , != , < , > , <= , >=
Assignment
= , += , -‐= , *= , /= , %= , &= , | = , ^= , <<= , >>=
Type information
is , sizeof , typeof, as
Indirection and Address
* , -‐> , [] , &
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Dividing a Integral Type with zero (Integral Division Operator) throws DivideByZeroException
•
Floating Point Division by zero is not a runtime exception but the value would be either PositiveInfinity (if numerator is greater than zero) or NegativeInfinity (if numerator is less than zero) or NaN (if numerator is also zero)
Using Conditional operator n = 10; int m = n++; //m=n; n=n+1 -‐ Post Increment Console.WriteLine(n + " " + m); m = ++n; //n=n+1; m=n -‐ Pre Increment Console.WriteLine(n + " " + m); //?: Conditional Operator (VB: IIf) int max; max = n > m ? n : m; //?: Operator
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Co ntrol Statements If else-‐statement syntax: if (BooleanExpression) { statement; } else if (Boolean-‐Expression) { statement; } else { statement; } Program to print if the command line argument provided is an odd number or even number using System; using System; class Program { public static void Main(string[] args) { int n; if (args.Length == 0) Console.WriteLine("Please provide a number"); else if (!int.TryParse(args[0], out n)) Console.WriteLine("Not a number"); else if (int.Parse(args[0]) % 2 == 0) Console.WriteLine("Even number"); else Console.WriteLine("Odd number"); } } Code: 3.3 C# Note:
To execute above program correctly, supply valid integers in command line arguments. Right click on Project -‐> Select Properties -‐> Click on Debug tab and enter few values in “Command line arguments” section seperated by spaces. For this example we have used the values: 2 3
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Here is the output of executing above code:
Fig: 3.2 Switch statement syntax: switch (expr) //expr can only integral type / char / string { case 0: //value of case must be a constant. statements; goto default; // or break can be used. case 1: case 2: statements; break; //break must be preset after every case with statements default: statements; break; //break must be present after default also. } Task: Write a program to print grade of the person based on the marks scored. while…..loop statement syntax: while (BooleanExpression) { Statements; } do { Statements } while (BooleanExpression) }
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Program to Print the table of any number read from the keyboard. using System; class Program { public static void Main() { int n; Console.Write("Table of: "); n = int.Parse(Console.ReadLine()); string s = ""; for (int i = 1; i <= 10; i++) s += n + "*" + i + "=" + n * i + "\n"; Console.WriteLine(s); } } Code: 3.4 C# Here is the output of executing above code:
Fig: 3.3 for statement syntax: for ( initializer; condition; iterator ) { statements; } Sample program implementing for loops – Example 1 using System; class Program { static void Main(string[] args) { for (int i = 0; i < 3; i++)
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{ for (int j = 0; j < 3; j++) { if (i == j) break; Console.WriteLine(i + " " + j); } } } } Code: 3.5 C# Here is the output of executing above code:
Fig: 3.4 Sample program implementing for loops – Example 2 using System; class Program { static void Main(string[] args) { for (int i = 0; i < 10; i++) { if (i == 7) break; if (i == 3) continue; Console.WriteLine(i); } } } Code: 3.6 C# Here is the output of executing above code:
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Fig: 3.5 Program to show the Pyramid of Numbers using System; class Program { static void Main(string[] args) { int k = 0; for (int i = 0; i < 4; i++) { for (int j = 0; j <= i; j++) Console.Write(k++ + "\t"); Console.WriteLine(); } } } Code: 3.7 C# Here is the output of executing above code:
Fig: 3.6
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Foreach statements syntax: foreach (DataType identifier in
) { embedded-‐statements; } Program to print all command line arguments using System; class Program { static void Main(string[] args) { foreach (string s in args) Console.WriteLine(s); } } Code: 3.8 C#
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Working with Arrays 1
Arrays are reference types and thus are allocated memory on heap.
2
Every element of an array is automatically initialized to a default value based on its data type.
3
They are always dynamic because we can SET the size of the arrays at runtime.
4
Size of array can never be changed at runtime.
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Trying to access an element of array with invalid index throws IndexOutofRangeException Exception.
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All arrays irrespective of their type are by default inherited from System. Array class
Single-‐Dimensional Arrays int [] myArray = new int [5]; string []myStringArray = new string[5]; When you initialize an array upon declaration, it is possible to use the following shortcuts: int[] myArray = {1, 3, 5, 7, 9}; string[] weekDays = {"Sun", "Sat", "Mon", "Tue"}; It is possible to declare an array variable without initialization, but you must use the new operator when you assign an array to this variable. For example: int[] myArray; myArray = new int[] {1, 3, 5, 7, 9}; // OK myArray = {1, 3, 5, 7, 9}; // Error weekdays = new string[] {“Sunday”, “Monday”, “Tuesday”}; Multi-‐Dimensional Arrays int[,] myArray = new int[4,2]; Also, the following declaration creates an array of three dimensions, 4, 2, and 3: int[,,] myArray = new int [4,2,3]; You can initialize the array upon declaration as shown in the following example: int[,] myArray = new int[,] {{1,2}, {3,4}, {5,6}, {7,8}}; You can also initialize the array without specifying the rank: int[,] myArray = {{1,2}, {3,4}, {5,6}, {7,8}}; If you choose to declare an array variable without initialization, you must use the new operator to assign an array to the variable. For example: int[,] myArray; myArray = new int[,] {{1,2}, {3,4}, {5,6}, {7,8}}; // OK myArray = {{1,2}, {3,4}, {5,6}, {7,8}}; // Error Program to use arrays: using System; class Program { static void Main(string[] args) { int[] ar = new int[] { 1, 2, 3, 4 }; Console.WriteLine(ar.Length); Console.WriteLine(ar.Rank); //Prints Number of Dimensions in array. foreach (int n in ar)
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Console.WriteLine(n); } } Code: 3.9 C# Here is the output of executing above code:
Fig: 3.7 Program: To read a list of numbers separated by space and print the Average of all those numbers. using System; class ProgramForMaxOfAnyNumbers { static void Main(string[] args) { string str = Console.ReadLine(); string[] ar = str.Split(' '); int sum = 0; for (int i = 0; i < ar.Length; i++) { sum += int.Parse(ar[i]); Console.WriteLine(ar[i]); } Console.WriteLine("Average: " + 1.0 * sum / ar.Length); } } Code: 3.10 C#
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Here is the output of executing above code:
Fig: 3.8 Program: To read length and data for an array from keyboard print the same. using System; class ProgramForMaxOfAnyNumbers { static void Main() { Console.Write("Enter the array length: "); int n; n = int.Parse(Console.ReadLine()); int[] ar = new int[n]; for (int i = 0; i < n; i++) { Console.Write("Enter the " + i + "th value: "); ar[i] = int.Parse(Console.ReadLine()); } for (int i = 0; i < ar.Length; i++) { Console.Write(ar[i] + " "); } } } Code: 3.11 C#
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Here is the output of executing above code:
Fig: 3.9
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Working with Methods Working with Methods Method Overloading: 1
Having two or more methods with same name and different parameters.
2
Parameters must be different either in their data type or in their count.
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Method cannot be overloaded based on Return Type or ByVal/ByRef or Parameter names.
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Call to the Overloaded method is resolved at compile time and is done based on data type and count of arguments passed to the method.
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While resolving the called method, the compiler searches for a direct match of arguments and parameters. Only if a direct match is not available it would then use nearest match for resolving the call.
Method overloading using System; class Program { public static void Main() { int res = Add(10, 2); Console.WriteLine(res.ToString()); string str; str = Add("Deccan", "soft"); Console.WriteLine(str); } static int Add(int a, int b) { return Add(a, b, 0); } static int Add(int a, int b, int c) { return a + b + c; } static string Add(string s1, string s2) { return s1 + s2; } } Code: 3.12 C#
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Here is the output of executing above code:
Fig: 3.10 Params Parameters: 1. Only Parameters which are of type array (of any data type) can be declared as params 2. If parameter is declared as params either a reference to the array can be passed as argument or 0 or more individual values can be passed to it. 3. Only one parameter of a method can be declared as params parameter. 4. It must be last parameter in the list of parameters for a given method. 5. If we have other parameters in the list they must be before the params parameter and they cannot be declared as optional. using System; class Program { public static void Main() { int res = Add(10, 2); int[] mar = { 1, 2, 3, 4 }; res = Add(mar); Console.WriteLine(res.ToString()); res = Add(); res = Add(1, 2, 3, 4, 5); res = Add(1, 2, 3, 4, 5, 6); res = Add(1, 2, 3, 4, 5, 6, 7); Console.WriteLine(res.ToString()); } static int Add(params int[] ar) { int sum = 0; foreach (int n in ar) sum += n; return sum; } } Code: 3.13 C# Here is the output of executing above code:
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Fig: 3.11 Pass by value and reference example using System; class Program { public static void Main() { int n1, n2, n3; n1 = n3 = 10; Foo(n1, out n2, ref n3); Console.WriteLine(n1 + " " + n2 + " " + n3); } static void Foo(int a, out int b, ref int c) { a++; b = 20; c++; } } Code: 3.14 C# Here is the output of executing above code:
Fig: 3.13
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The argument “n2” is passed by reference to “b”, i.e. both “b” and “n2” reference to same memory and hence change made to “b” is also reflected in “n2”. Out parameter must be initialized in the method and are generally used in situations where we want to return more than one value from the method. If a method has return type anything other than “void”, all code paths in it must return a value. The example below compilation error because if a==0 nothing is mentioned as return value: static int Foo(int a) { if (a != 0) return a; }
Summary In this section we have covered most of the C# language structures that includes: Datatypes declaration & initialization, conditional and looping structures, working with arrays & methods and enumerated datatypes.
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