April 2016

8:42 am

C# - Loops

There may be a situation, when you need to execute a block of code several number of times. In general, the statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.
Programming languages provide various control structures that allow for more complicated execution paths.
A loop statement allows us to execute a statement or a group of statements multiple times and following is the general from of a loop statement in most of the programming languages:
Loop Architecture
C# provides following types of loop to handle looping requirements. Click the following links to check their detail.
Loop TypeDescription
It repeats a statement or a group of statements while a given condition is true. It tests the condition before executing the loop body.
It executes a sequence of statements multiple times and abbreviates the code that manages the loop variable.
It is similar to a while statement, except that it tests the condition at the end of the loop body
You can use one or more loop inside any another while, for or do..while loop.

Loop Control Statements

Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.
C# provides the following control statements. Click the following links to check their details.
Control StatementDescription
Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch.
Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating.

Infinite Loop

A loop becomes infinite loop if a condition never becomes false. The for loop is traditionally used for this purpose. Since none of the three expressions that form the for loop are required, you can make an endless loop by leaving the conditional expression empty.

Example

using System;
namespace Loops
{
   class Program
   {
      static void Main(string[] args)
      {
         for (; ; )
         {
            Console.WriteLine("Hey! I am Trapped");
         }
      }
   }
}
When the conditional expression is absent, it is assumed to be true. You may have an initialization and increment expression, but programmers more commonly use the for(;;) construct to signify an infinite loop.
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8:41 am



Decision making structures requires the programmer to specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.
Following is the general from of a typical decision making structure found in most of the programming languages:
Decision making statements in C#
C# provides following types of decision making statements. Click the following links to check their detail.
StatementDescription
An if statement consists of a boolean expression followed by one or more statements.
An if statement can be followed by an optional else statement, which executes when the boolean expression is false.
You can use one if or else if statement inside another if or else if statement(s).
A switch statement allows a variable to be tested for equality against a list of values.
You can use one switch statement inside anotherswitch statement(s).

The ? : Operator:

We have covered conditional operator ? : in previous chapter which can be used to replace if...else statements. It has the following general form:
Exp1 ? Exp2 : Exp3;
Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.
The value of a ? expression is determined as follows: Exp1 is evaluated. If it is true, then Exp2 is evaluated and becomes the value of the entire ? expression. If Exp1 is false, then Exp3 is evaluated and its value becomes the value of the expression.
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8:41 am

C# - Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C# has rich set of built-in operators and provides the following type of operators:
  • Arithmetic Operators
  • Relational Operators
  • Logical Operators
  • Bitwise Operators
  • Assignment Operators
  • Misc Operators
This tutorial explains the arithmetic, relational, logical, bitwise, assignment, and other operators one by one.

Arithmetic Operators

Following table shows all the arithmetic operators supported by C#. Assume variable A holds 10 and variable B holds 20 then:
OperatorDescriptionExample
+Adds two operandsA + B = 30
-Subtracts second operand from the firstA - B = -10
*Multiplies both operandsA * B = 200
/Divides numerator by de-numeratorB / A = 2
%Modulus Operator and remainder of after an integer divisionB % A = 0
++Increment operator increases integer value by oneA++ = 11
--Decrement operator decreases integer value by oneA-- = 9

Relational Operators

Following table shows all the relational operators supported by C#. Assume variable A holds 10 and variable B holds 20, then:
OperatorDescriptionExample
==Checks if the values of two operands are equal or not, if yes then condition becomes true.(A == B) is not true.
!=Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.(A != B) is true.
>Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.(A > B) is not true.
<Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.(A < B) is true.
>=Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.(A >= B) is not true.
<=Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.(A <= B) is true.

Logical Operators

Following table shows all the logical operators supported by C#. Assume variable A holds Boolean value true and variable B holds Boolean value false, then:
OperatorDescriptionExample
&&Called Logical AND operator. If both the operands are non zero then condition becomes true.(A && B) is false.
||Called Logical OR Operator. If any of the two operands is non zero then condition becomes true.(A || B) is true.
!Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.!(A && B) is true.

Bitwise Operators

Bitwise operator works on bits and perform bit by bit operation. The truth tables for &, |, and ^ are as follows:
pqp & qp | qp ^ q
00000
01011
11110
10011
Assume if A = 60; and B = 13; then in the binary format they are as follows:
A = 0011 1100
B = 0000 1101
-----------------
A&B = 0000 1100
A|B = 0011 1101
A^B = 0011 0001
~A  = 1100 0011
The Bitwise operators supported by C# are listed in the following table. Assume variable A holds 60 and variable B holds 13, then:
OperatorDescriptionExample
&Binary AND Operator copies a bit to the result if it exists in both operands.(A & B) = 12, which is 0000 1100
|Binary OR Operator copies a bit if it exists in either operand.(A | B) = 61, which is 0011 1101
^Binary XOR Operator copies the bit if it is set in one operand but not both.(A ^ B) = 49, which is 0011 0001
~Binary Ones Complement Operator is unary and has the effect of 'flipping' bits.(~A ) = 61, which is 1100 0011 in 2's complement due to a signed binary number.
<<Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand.A << 2 = 240, which is 1111 0000
>>Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.A >> 2 = 15, which is 0000 1111

Assignment Operators

There are following assignment operators supported by C#:
OperatorDescriptionExample
=Simple assignment operator, Assigns values from right side operands to left side operandC = A + B assigns value of A + B into C
+=Add AND assignment operator, It adds right operand to the left operand and assign the result to left operandC += A is equivalent to C = C + A
-=Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operandC -= A is equivalent to C = C - A
*=Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operandC *= A is equivalent to C = C * A
/=Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operandC /= A is equivalent to C = C / A
%=Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operandC %= A is equivalent to C = C % A
<<=Left shift AND assignment operatorC <<= 2 is same as C = C << 2
>>=Right shift AND assignment operatorC >>= 2 is same as C = C >> 2
&=Bitwise AND assignment operatorC &= 2 is same as C = C & 2
^=bitwise exclusive OR and assignment operatorC ^= 2 is same as C = C ^ 2
|=bitwise inclusive OR and assignment operatorC |= 2 is same as C = C | 2

Miscillaneous Operators

There are few other important operators including sizeof, typeof and ? :supported by C#.
OperatorDescriptionExample
sizeof()Returns the size of a data type.sizeof(int), returns 4.
typeof()Returns the type of a class.typeof(StreamReader);
&Returns the address of an variable.&a; returns actual address of the variable.
*Pointer to a variable.*a; creates pointer named 'a' to a variable.
? :Conditional ExpressionIf Condition is true ? Then value X : Otherwise value Y
isDetermines whether an object is of a certain type.If( Ford is Car) // checks if Ford is an object of the Car class.
asCast without raising an exception if the cast fails.Object obj = new StringReader("Hello");
StringReader r = obj as StringReader;

Operator Precedence in C#

Operator precedence determines the grouping of terms in an expression. This affects evaluation of an expression. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator.
For example x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so the first evaluation takes place for 3*2 and then 7 is added into it.
Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators are evaluated first.
CategoryOperatorAssociativity
Postfix() [] -> . ++ - -Left to right
Unary+ - ! ~ ++ - - (type)* & sizeofRight to left
Multiplicative* / %Left to right
Additive+ -Left to right
Shift<< >>Left to right
Relational< <= > >=Left to right
Equality== !=Left to right
Bitwise AND&Left to right
Bitwise XOR^Left to right
Bitwise OR|Left to right
Logical AND&&Left to right
Logical OR||Left to right
Conditional?:Right to left
Assignment= += -= *= /= %=>>= <<= &= ^= |=Right to left
Comma,Left to right
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8:40 am

C# - Constants and Literals

The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.
The constants are treated just like regular variables except that their values cannot be modified after their definition.

Integer Literals

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and no prefix id for decimal.
An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.
Here are some examples of integer literals:
212         /* Legal */
215u        /* Legal */
0xFeeL      /* Legal */
078         /* Illegal: 8 is not an octal digit */
032UU       /* Illegal: cannot repeat a suffix */
Following are other examples of various types of Integer literals:
85         /* decimal */
0213       /* octal */
0x4b       /* hexadecimal */
30         /* int */
30u        /* unsigned int */
30l        /* long */
30ul       /* unsigned long */

Floating-point Literals

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.
Here are some examples of floating-point literals:
3.14159       /* Legal */
314159E-5L    /* Legal */
510E          /* Illegal: incomplete exponent */
210f          /* Illegal: no decimal or exponent */
.e55          /* Illegal: missing integer or fraction */
While representing in decimal form, you must include the decimal point, the exponent, or both; and while representing using exponential form you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.

Character Constants

Character literals are enclosed in single quotes. For example, 'x' and can be stored in a simple variable of char type. A character literal can be a plain character (such as 'x'), an escape sequence (such as '\t'), or a universal character (such as '\u02C0').
There are certain characters in C# when they are preceded by a backslash. The have special meaning and they are used to represent like newline (\n) or tab (\t). Here, is a list of some of such escape sequence codes:
Escape sequenceMeaning
\\\ character
\'' character
\"" character
\?? character
\aAlert or bell
\bBackspace
\fForm feed
\nNewline
\rCarriage return
\tHorizontal tab
\vVertical tab
\oooOctal number of one to three digits
\xhh . . .Hexadecimal number of one or more digits
Following is the example to show few escape sequence characters:
using System;
namespace EscapeChar 
{
   class Program
   {
      static void Main(string[] args)
      {
         Console.WriteLine("Hello\tWorld\n\n");
         Console.ReadLine();
      }
   }
}
When the above code is compiled and executed, it produces the following result:
Hello   World

String Literals

String literals or constants are enclosed in double quotes "" or with @"". A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.
You can break a long line into multiple lines using string literals and separating the parts using whitespaces.
Here are some examples of string literals. All the three forms are identical strings.
"hello, dear"
"hello, \
dear"
"hello, " "d" "ear"
@"hello dear"

Defining Constants

Constants are defined using the const keyword. Syntax for defining a constant is:
const <data_type> <constant_name> = value;
The following program demonstrates defining and using a constant in your program:
using System;
namespace DeclaringConstants
{
    class Program
    {
        static void Main(string[] args)
        {
            const double pi = 3.14159;   
            
            // constant declaration 
            double r;
            Console.WriteLine("Enter Radius: ");
            r = Convert.ToDouble(Console.ReadLine());
            double areaCircle = pi * r * r;
            Console.WriteLine("Radius: {0}, Area: {1}", r, areaCircle);
            Console.ReadLine();
        }
    }
}
When the above code is compiled and executed, it produces the following result:
Enter Radius: 
3
Radius: 3, Area: 28.27431
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