C# 4 and .NET 4

flow Control ❘ 37
The output from this is:
s1 is a string
s2 is a string
s1 is now another string
s2 is now a string
Changing the value of s1 has no effect on s2, contrary to what you’d expect with a reference type! What’s
happening here is that when s1 is initialized with the value a string, a new string object is allocated on
the heap. When s2 is initialized, the reference points to this same object, so s2 also has the value a string.
However, when you now change the value of s1, instead of replacing the original value, a new object will
be allocated on the heap for the new value. The s2 variable will still point to the original object, so its value
is unchanged. Under the hood, this happens as a result of operator overloading, a topic that is explored in
Chapter 7. In general, the string class has been implemented so that its semantics follow what you would
normally intuitively expect for a string.
String literals are enclosed in double quotation marks (”.”); if you attempt to enclose a string in single
quotation marks, the compiler will take the value as a char, and throw an error. C# strings can contain
the same Unicode and hexadecimal escape sequences as chars. Because these escape sequences start with
a backslash, you can’t use this character unescaped in a string. Instead, you need to escape it with two
backslashes (\\):
string filepath = "C:\\ProCSharp\\First.cs";
Even if you are confident that you can remember to do this all the time, typing all those double backslashes
can prove annoying. Fortunately, C# gives you an alternative. You can prefix a string literal with the at
character (@) and all the characters in it will be treated at face value; they won’t be interpreted as escape
sequences:
string filepath = @"C:\ProCSharp\First.cs";
This even allows you to include line breaks in your string literals:
string jabberwocky = @"'Twas brillig and the slithy toves
Did gyre and gimble in the wabe.";
Then the value of jabberwocky would be this:
'Twas brillig and the slithy toves
Did gyre and gimble in the wabe.
floW ConTrol
This section looks at the real nuts and bolts of the language: the statements that allow you to control the
flow of your program rather than executing every line of code in the order it appears in the program.
Conditional statements
Conditional statements allow you to branch your code depending on whether certain conditions are met or
on the value of an expression. C# has two constructs for branching code — the if statement, which allows
you to test whether a specific condition is met, and the switch statement, which allows you to compare an
expression with a number of different values.
The if statement
For conditional branching, C# inherits the C and C++ if.else construct. The syntax should be fairly
intuitive for anyone who has done any programming with a procedural language:
if (condition)
statement(s)
else
statement(s)
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