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vc的电子书

	<BR>
	<B>3. If a function doesn't return a value, how do you declare the function?</B><BR>
	<BR>
	Declare the function to return <TT>void</TT>.<BR>
	<BR>
	<B>4. If you don't declare a return value, what type of return value is assumed?</B><BR>
	<BR>
	Any function that does not explicitly declare a return type returns <TT>int</TT>.<BR>
	<BR>
	<B>5. What is a local variable?</B><BR>
	<BR>
	A local variable is a variable passed into or declared within a block, typically
	a function. It is visible only within the block.<BR>
	<BR>
	<B>6. What is scope?</B><BR>
	<BR>
	Scope refers to the visibility and lifetime of local and global variables. Scope
	is usually established by a set of braces.<BR>
	<BR>
	<B>7. What is recursion?</B><BR>
	<BR>
	Recursion generally refers to the ability of a function to call itself.<BR>
	<BR>
	<B>8. When should you use global variables?</B><BR>
	<BR>
	Global variables are typically used when many functions need access to the same data.
	Global variables are very rare in C++; once you know how to create static class variables,
	you will almost never create global variables.<BR>
	<BR>
	<B>9. What is function overloading?</B><BR>
	<BR>
	Function overloading is the ability to write more than one function with the same
	name, distinguished by the number or type of the parameters.<BR>
	<BR>
	<B>10. What is polymorphism?</B><BR>
	<BR>
	Polymorphism is the ability to treat many objects of differing but related types
	without regard to their differences. In C++, polymorphism is accomplished by using
	class derivation and virtual functions.
</DL>

<H4 ALIGN="CENTER"><A NAME="Heading17"></A><FONT COLOR="#000077">Exercises</FONT></H4>

<DL>
	<DD><B>1.</B> Write the prototype for a function named <TT>Perimeter</TT>, which
	returns an <TT>unsigned long int</TT> and which takes two parameters, both <TT>unsigned
	short</TT> <TT>int</TT>s.<BR>
	u<TT>nsigned long int</TT> <TT>Perimeter</TT>(<TT>unsigned short int</TT>, <TT>unsigned
	short int</TT>);<BR>
	<BR>
	<B>2.</B> Write the definition of the function <TT>Perimeter</TT> as described in
	Exercise 1. The two parameters represent the length and width of a rectangle and
	have the function return the perimeter (twice the length plus twice the width).
</DL>

<PRE><FONT COLOR="#0066FF"><TT>unsigned long int Perimeter</TT>(<TT>unsigned short int length</TT>, <TT>unsigned short int width</TT>)</FONT>
<FONT COLOR="#0066FF">
{
  return 2*length + 2*width;
}
</FONT></PRE>

<DL>
	<DD><B>3</B>. BUG BUSTERS: What is wrong with the function?
</DL>

<PRE><FONT COLOR="#0066FF">#include &lt;iostream.h&gt;
void myFunc(unsigned short int x);
int main()
{
    unsigned short int x, y;
    y = myFunc(int);
    cout &lt;&lt; &quot;x: &quot; &lt;&lt; x &lt;&lt; &quot; y: &quot; &lt;&lt; y &lt;&lt; &quot;\n&quot;;
return 0;
}

void myFunc(unsigned short int x)
{
    return (4*x);
}</FONT></PRE>

<DL>
	<DD>The function is declared to return <TT>void</TT> and it cannot return a value.<BR>
	<BR>
	<B>4.</B> BUG BUSTERS: What is wrong with the function?
</DL>

<PRE><FONT COLOR="#0066FF">#include &lt;iostream.h&gt;
int myFunc(unsigned short int x);
int main()
{
    unsigned short int x, y;
    y = myFunc(int);
    cout &lt;&lt; &quot;x: &quot; &lt;&lt; x &lt;&lt; &quot; y: &quot; &lt;&lt; y &lt;&lt; &quot;\n&quot;;
return 0;
}

int myFunc(unsigned short int x)
{
    return (4*x);
}
</FONT></PRE>

<DL>
	<DD>This function would be fine, but there is a semicolon at the end of the function
	definition's header.<BR>
	<BR>
	<B>5.</B> Write a function that takes two <TT>unsigned short</TT> <TT>int</TT> arguments
	and returns the result of dividing the first by the second. Do not do the division
	if the second number is <TT>0</TT>, but do return <TT>-1</TT>.<BR>
	<TT>short int Divider</TT>(<TT>unsigned short int valOne</TT>, <TT>unsigned short
	int valTwo</TT>)
</DL>

<PRE><FONT COLOR="#0066FF">{
    if (valTwo == 0)
          return -1;
    else
          return valOne / valTwo;
}
</FONT></PRE>

<DL>
	<DD><B>6.</B> Write a program that asks the user for two numbers and calls the function
	you wrote in Exercise 5. Print the answer, or print an error message if you get <TT>-1</TT>.
</DL>

<PRE><FONT COLOR="#0066FF">#include &lt;iostream.h&gt;
typedef unsigned short int USHORT;
typedef unsigned long int ULONG;
short int Divider(
unsigned short int valone,
unsigned short int valtwo);
int main()
{
    USHORT one, two;
    short int answer;
    cout &lt;&lt; &quot;Enter two numbers.\n Number one: &quot;;
    cin &gt;&gt; one;
    cout &lt;&lt; &quot;Number two: &quot;;
    cin &gt;&gt; two;
    answer = Divider(one, two);
    if (answer &gt; -1)
       cout &lt;&lt; &quot;Answer: &quot; &lt;&lt; answer;
    else
       cout &lt;&lt; &quot;Error, can't divide by zero!&quot;;
return 0;
}
</FONT></PRE>

<DL>
	<DD><B>7. </B>Write a program that asks for a number and a power. Write a recursive
	function that takes the number to the power. Thus, if the number is 2 and the power
	is 4, the function will return <TT>16</TT>.
</DL>

<PRE><FONT COLOR="#0066FF">#include &lt;iostream.h&gt;
typedef unsigned short USHORT;
typedef unsigned long ULONG;
ULONG GetPower(USHORT n, USHORT power);
int main()
{
   USHORT number, power;
   ULONG answer;
   cout &lt;&lt; &quot;Enter a number: &quot;;
   cin &gt;&gt; number;
   cout &lt;&lt; &quot;To what power? &quot;;
   cin &gt;&gt; power;
   answer = GetPower(number,power);
   cout &lt;&lt; number &lt;&lt; &quot; to the &quot; &lt;&lt; power &lt;&lt; &quot;th power is &quot; &lt;&lt;
answer &lt;&lt; endl;
return 0;
}

ULONG GetPower(USHORT n, USHORT power)
{
    if(power == 1)
     return n;
    else
       return (n * GetPower(n,power-1));
}
</FONT></PRE>
<H3 ALIGN="CENTER"><FONT COLOR="#0066FF"></FONT></H3>
<H3><A NAME="Heading18"></A><FONT COLOR="#000077">Day 6</FONT></H3>
<H4 ALIGN="CENTER"><A NAME="Heading19"></A><FONT COLOR="#000077">Quiz</FONT></H4>

<DL>
	<DD><B>1. What is the dot operator, and what is it used for?</B><BR>
	<BR>
	The dot operator is the period (<TT>.</TT>). It is used to access the members of
	the class.<BR>
	<BR>
	<B>2. Which sets aside memory--declaration or definition?</B><BR>
	<BR>
	Definitions of variables set aside memory. Declarations of classes don't set aside
	memory.<BR>
	<BR>
	<B>3. Is the declaration of a class its interface or its implementation?</B><BR>
	<BR>
	The declaration of a class is its interface; it tells clients of the class how to
	interact with the class. The implementation of the class is the set of member functions
	stored--usually in a related CPP file.<BR>
	<BR>
	<B>4. What is the difference between public and private data members?</B><BR>
	<BR>
	Public data members can be accessed by clients of the class. Private data members
	can be accessed only by member functions of the class.<BR>
	<BR>
	<B>5. Can member functions be private?<BR>
	</B><BR>
	Yes. Both member functions and member data can be private.<BR>
	<BR>
	<B>6. Can member data be public?</B><BR>
	<BR>
	Although member data can be public, it is good programming practice to make it private
	and to provide public accessor functions to the data.<BR>
	<BR>
	<B>7. If you declare two <TT>Cat</TT> objects, can they have different values in
	their <TT>itsAge</TT> member data?</B><BR>
	<BR>
	Yes. Each object of a class has its own data members.<BR>
	<BR>
	<B>8. Do class declarations end with a semicolon? Do class method definitions?</B><BR>
	<BR>
	Declarations end with a semicolon after the closing brace; function definitions do
	not.<BR>
	<BR>
	<B>9. What would the header for a <TT>Cat</TT> function, <TT>Meow</TT>, that takes
	no parameters and returns <TT>void</TT> look like?<BR>
	</B><BR>
	The header for a <TT>Cat</TT> function, <TT>Meow()</TT>, that takes no parameters
	and returns <TT>void</TT> looks like this:
</DL>

<PRE><FONT COLOR="#0066FF">void Cat::Meow()
</FONT></PRE>

<DL>
	<DD><B>10. What function is called to initialize a class?<BR>
	</B><BR>
	The constructor is called to initialize a class.
</DL>

<H4 ALIGN="CENTER"><A NAME="Heading20"></A><FONT COLOR="#000077">Exercises</FONT></H4>

<DL>
	<DD><B>1. </B>Write the code that declares a class called <TT>Employee</TT> with
	these data members: <TT>age</TT>, <TT>yearsOfService</TT>, and <TT>Salary</TT>.
</DL>

<PRE><FONT COLOR="#0066FF">class Employee
{
    int Age;
    int YearsOfService;
    int Salary;
};
</FONT></PRE>

<DL>
	<DD><B>2.</B> Rewrite the <TT>Employee</TT> class to make the data members private,
	and provide public accessor methods to get and set each of the data members.
</DL>

<PRE><FONT COLOR="#0066FF">class Employee
{
public:
    int GetAge() const;
    void SetAge(int age);
    int GetYearsOfService()const;
    void SetYearsOfService(int years);
    int GetSalary()const;
    void SetSalary(int salary);

private:
    int Age;
    int YearsOfService;
    int Salary;
};
</FONT></PRE>

<DL>
	<DD><B>3.</B> Write a program with the <TT>Employee</TT> class that makes two <TT>Employee</TT>s;
	sets their <TT>age</TT>, <TT>YearsOfService</TT>, and <TT>Salary</TT>; and prints
	their values.
</DL>

<PRE><FONT COLOR="#0066FF">main()
{
    Employee John;
    Employee Sally;
    John.SetAge(30);
    John.SetYearsOfService(5);
    John.SetSalary(50000);

    Sally.SetAge(32);
    Sally.SetYearsOfService(8);
    Sally.SetSalary(40000);

    cout &lt;&lt; &quot;At AcmeSexist company, John and Sally have the same
job.\n&quot;;
    cout &lt;&lt; &quot;John is &quot; &lt;&lt; John.GetAge() &lt;&lt; &quot; years old and he has
been with&quot;;
    cout &lt;&lt; &quot;the firm for &quot; &lt;&lt; John.GetYearsOfService &lt;&lt; &quot;
years.\n&quot;;
    cout &lt;&lt; &quot;John earns $&quot; &lt;&lt; John.GetSalary &lt;&lt; &quot; dollars per
year.\n\n&quot;;
    cout &lt;&lt; &quot;Sally, on the other hand is &quot; &lt;&lt; Sally.GetAge() &lt;&lt; &quot;
years old and has&quot;;
    cout &lt;&lt; &quot;been with the company &quot; &lt;&lt; Sally.GetYearsOfService;
    cout &lt;&lt; &quot; years. Yet Sally only makes $&quot; &lt;&lt; Sally.GetSalary();
    cout &lt;&lt; &quot; dollars per year!  Something here is unfair.&quot;;
</FONT></PRE>

<DL>
	<DD><B>4.</B> Continuing from Exercise 3, provide a method of <TT>Employee</TT> that
	reports how many thousands of dollars the employee earns, rounded to the nearest
	1,000.
</DL>

<PRE><FONT COLOR="#0066FF">float Employee:GetRoundedThousands()const
{
    return Salary / 1000;
}
</FONT></PRE>

<DL>
	<DD><B>5. </B>Change the <TT>Employee</TT> class so that you can initialize <TT>age</TT>,
	<TT>YearsOfService</TT>, and <TT>Salary</TT> when you create the employee.
</DL>

<PRE><FONT COLOR="#0066FF">class Employee
{
public:

    Employee(int age, int yearsOfService, int salary);
    int GetAge()const;
    void SetAge(int age);
    int GetYearsOfService()const;
    void SetYearsOfService(int years);
    int GetSalary()const;
    void SetSalary(int salary);

private:
    int Age;
    int YearsOfService;
    int Salary;
};
</FONT></PRE>

<DL>
	<DD><B>6.</B> BUG BUSTERS: What is wrong with the following declaration?
</DL>

<PRE><FONT COLOR="#0066FF">class Square
{
public:
    int Side;
}</FONT></PRE>

<DL>
	<DD>Class declarations must end with a semicolon.<BR>
	<BR>
	<B>7</B>. BUG BUSTERS: Why isn't the following class declaration very useful?
</DL>

<PRE><FONT COLOR="#0066FF">class Cat
{
    int GetAge()const;
private:
    int itsAge;
};</FONT></PRE>

<DL>
	<DD>The accessor <TT>GetAge()</TT> is private. Remember: All class members are private
	unless you say otherwise.<BR>
	<BR>
	<B>8</B>. BUG BUSTERS: What three bugs in this code will the compiler find?
</DL>

<PRE><FONT COLOR="#0066FF">class  TV
{
public:
    void SetStation(int Station);
    int GetStation() const;
private:
    int itsStation;
};

main()
{
    TV myTV;
    myTV.itsStation = 9;
    TV.SetStation(10);
    TV myOtherTv(2);
}
</FONT></PRE>

<DL>
	<DD>You can't access <TT>itsStation</TT> directly. It is private.<BR>
	You can't call <TT>SetStation()</TT> on the class. You can call <TT>SetStation()</TT>
	only on objects.<BR>
	You can't initialize <TT>itsStation</TT> because there is no matching constructor.
</DL>

<H3 ALIGN="CENTER"></H3>
<H3><A NAME="Heading21"></A><FONT COLOR="#000077">Day 7</FONT></H3>
<H4 ALIGN="CENTER"><A NAME="Heading22"></A><FONT COLOR="#000077">Quiz</FONT></H4>

<DL>
	<DD><B>1. How do I initialize more than one variable in a <TT>for</TT> loop?</B><BR>
	<BR>
	Separate the initializations with commas, such as
</DL>

<PRE><FONT COLOR="#0066FF">for (x = 0, y = 10; x &lt; 100; x++, y++)
</FONT></PRE>

<DL>
	<DD><B>2. Why is <TT>goto</TT> avoided?<BR>
	</B><TT><BR>
	goto</TT> jumps in any direction to any arbitrary line of code. This makes for source
	code that is difficult to understand and therefore difficult to maintain.<BR>
	<BR>
	<B>3. Is it possible to write a <TT>for</TT> loop with a body that is never executed?</B><BR>
	<BR>
	Yes, if the condition is <TT>FALSE</TT> after the initialization, the body of the
	<TT>for</TT> loop will never execute. Here's an example:
</DL>