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Subject: Statements - C# Nuts and Bolt - Beta2
Date: Wed, 29 Aug 2007 13:27:58 +0800
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<o:Created>2001-09-27T11:55:00Z</o:Created>
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<DIV class=3DSection1>
<P class=3DMsoNormal><IMG id=3D_x0000_i1025 height=3D48=20
src=3D"http://www.vijaymukhi.com/documents/books/csadv/bpb.jpg" =
width=3D64></P>
<P class=3DMsoNormal><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></P>
<P class=3DMsoNormal><SPAN=20
style=3D"FONT-SIZE: 15pt; COLOR: black; FONT-FAMILY: Garamond">Chapter=20
2</SPAN></P>
<P class=3DMsoNormal><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></P>
<P class=3DMsoNormal><SPAN=20
style=3D"FONT-SIZE: 26pt; COLOR: black; FONT-FAMILY: =
Garamond">Statements</SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">C# provides us with a =
countless=20
number of statements. Let us now understand each one of them in=20
detail.<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCprg><U>a.cs</U><o:p></o:p></P>
<P class=3DCprg>public class zzz <o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>public static void Main()<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>bool i =3D false;<o:p></o:p></P>
<P class=3DCprg>if ( i)<o:p></o:p></P>
<P class=3DCprg>int j =3D 40;<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCoutput><U>Compiler Errors</U><o:p></o:p></P>
<P class=3DCoutput>a.cs(7,1): error CS1023: Embedded statement cannot be =
a=20
declaration or labeled statement<o:p></o:p></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">It is not mandatory =
for the if=20
statement to have the {} if we want to limit its scope to only one line. =
However, we cannot have a variable declaration as the only line =
following it.=20
This is because if the condition results to false, the variable will =
never be=20
created. <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">The value of the =
variable i can=20
only be determined at run time and thus C# flags an error. The line =
following=20
the if condition, int j =3D 40;<SPAN style=3D"mso-spacerun: yes"> =
</SPAN>is=20
called an embedded statement.<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">Every C# statement =
has an=20
end-point. The end-point is intuitively the end of the statement. If a =
statement=20
can be executed, we call it a reachable statement else it is =
unreachable.=20
Unreachable statements for some reason flag a warning and not an error. =
To=20
figure out whether a statement is reachable or not, C# does flow =
analysis.=20
<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCprg><U>a.cs</U><o:p></o:p></P>
<P class=3DCprg>public class zzz <o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>public static void Main()<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>int i =3D 30;<o:p></o:p></P>
<P class=3DCprg>const int j =3D 30;<o:p></o:p></P>
<P class=3DCprg>if ( i =3D=3D 3)<o:p></o:p></P>
<P class=3DCprg>System.Console.WriteLine("hi");<o:p></o:p></P>
<P class=3DCprg>if ( j =3D=3D 3)<o:p></o:p></P>
<P class=3DCprg>System.Console.WriteLine("hi");<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCoutput><U>Compiler Warning</U><o:p></o:p></P>
<P class=3DCoutput>a.cs(10,1): warning CS0162: Unreachable code=20
detected<o:p></o:p></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">Two identical if =
statements. One=20
produces unreachable code whereas the second does not. In the case of =
variable=20
j, the compiler sees it as a const and therefore knows that its value =
will never=20
change. The if will always end in false, therefore, a warning.=20
<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">In the case of the =
first if, even=20
though the value of variable i is 30 and C# knows that it results in =
false, it=20
still believes that an act of God can change the value of variable i.=20
Consequently, no error but a mere warning is =
generated<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">As for the value of a =
const=20
variable, even God possesses no privilege to change it, hence the =
compiler pops=20
up a warning. The above rule is part of what goes under the moniker of =
flow=20
analysis. An end point should not be reached for a switch and a return=20
statement.<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">The if statement =
falls under the=20
set of selection statement. It executes statements depending upon the =
value of a=20
controlling expression.<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></SPAN></P>
<P class=3DCprg>if (x) if (y) F(); else G();<o:p></o:p></P>
<P class=3DCprg><![if =
!supportEmptyParas]><![endif]> <o:p></o:p></P>
<P class=3DCprg>if (x) {<o:p></o:p></P>
<P class=3DCprg><SPAN=20
style=3D"mso-tab-count: =
1"> =20
</SPAN>if (y) {<o:p></o:p></P>
<P class=3DCprg><SPAN=20
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