Note04

书：C++大学教程（第七版）
1. cmath头文件提供了能够进行通用数学计算的函数集合。

2. 数据类型

3. 标准库头文件



4. rand函数的原型在中
5. srand()和rand()
srand()就是给rand()提供种子seed，通常将时间作为种子；
srand(time(0));
如果srand每次输入的数值是一样的，那么每次运行产生的随机数也是一样的

srand( (unsigned)time( NULL ) ); /* Display 10 numbers. */ for( i = 0; i < 10;i++ )     printf( " %6d/n", rand() ); }

#include <iostream>#include <cstdlib>#include <ctime>using namespace std;int main(){    srand(time(0));    for (size_t i = 0; i < 100; i++)    {        if (i > 0 && i % 5 == 0)        {            cout << endl;        }        cout << rand()<<"\t";    }    system("pause");    return 0;}

1. 递归和迭代
   迭代使用循环结构，递归使用选择结构；迭代显示地使用循环结构，递归通过重复的函数调用实现循环；
2. 将指针传递给函数的4种方式：
   （1）指向非常量数据的非常量指针：具有最大的访问权限，如：int *countPtr；
   （2）指向常量数据的非常量指针：可以被修改以指向任何适当类型的其他数据项，但是不能通过该指针来修改它所指向的数据。可以用这种指针为函数接收数组实参，函数处理数组的每个元素，但不允许修改数据。形如：const int *countPtr；从右到左读作“countPtr是指向一个字符常量的指针”
   （3）指向非常量数据的常量指针：始终指向同一个内存位置，通过该指针可以修改这个位置上的数据。这就是数组名的默认情况，数组名是指向这个数组开始处的常量指针。使用数组名和数组下标，可以访问和修改数组中的所有元素。可以用来接收数组作为函数的实参，在函数中用数组下标表示法访问数组元素。声明为const的指针在声明时必须被初始化，如果指针是函数参数，他被传递给函数的指针初始化。形如：int * const ptr = &x;
   （4）指向常量数据的常量指针：具有最小的访问权限。这种指针总是指向内存中相同的位置，并且不能用该指针修改这个内存位置的数据。如果函数接收一个数组做参数，只是用数组下标表示法读取数组而不修改数组，那么应该用这种指针。形如：const int * const ptr = &x;从右大左读作“ptrr是指向一个整数常量的常量指针”。当试图修改ptr指向的数据和存储在该指针变量中的地址时，产生错误信息。注意：当程序试图间接引用ptr，或当程序试图输出ptr所指向的值时，不会发生错误。
3. 数组名是常量指针，总是指向数组的开头。如：b += 3；将引起错误；

int b[5];int *bPtr;bPtr = b;//等价于bPtr = &b[0];

第三个元素的值： *(b+2)
9. 函数指针

bool (* compare ) (int , int )

关键字bool表示所指向的函数返回一个bool值。文本(*compare)表示函数指针的名字（此处的*表明参数compare是一个指针）。文本（int，int）表示compare所指向的函数有两个整型参数。*compare的两边要加上圆括号，才能表示compare是一个函数指针。如果不加圆括号，该声明将变成下述形式：

bool * compare(int, int )

那么它表示一个接受两个整数做参数、并返回一个指向bool值的指针的函数。

(*compare)( work[ smallestOrLargest ], work[ index ] )

就想简介引用变量指针可以访问变量值一样，简介引用函数指针可以执行该函数。*compare两边的圆括号是必须的，如果没有，*运算符试图间接引用函数调用所返回的值。不间接引用函数指针，也可以调用该函数，如下所示：

compare( work[ smallestOrLargest ], work[ index ] )

这里将指针直接作为函数名使用。提倡通过指针调用函数的第一种方法，因为他显示地说明compare是一个函数指针，通过间接引用这个指针来调用函数。通过指针调用函数的第二种犯法使compare看起来好像是程序中的一个实际函数的名字。这会使程序的用户感到迷惑，他想看函数compare的定义，但却发现在文件中它并没有被定义。

// Multipurpose sorting program using function pointers.#include <iostream>#include <iomanip>using namespace std;// prototypesvoid selectionSort( int [], const int, bool (*)( int, int ) );void swap( int * const, int * const );   bool ascending( int, int ); // implements ascending orderbool descending( int, int ); // implements descending orderint main(){   const int arraySize = 10;   int order; // 1 = ascending, 2 = descending   int counter; // array index   int a[ arraySize ] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 };   cout << "Enter 1 to sort in ascending order,\n"       << "Enter 2 to sort in descending order: ";   cin >> order;   cout << "\nData items in original order\n";   // output original array   for ( counter = 0; counter < arraySize; counter++ )      cout << setw( 4 ) << a[ counter ];   // sort array in ascending order; pass function ascending    // as an argument to specify ascending sorting order   if ( order == 1 )    {      selectionSort( a, arraySize, ascending );      cout << "\nData items in ascending order\n";   } // end if   // sort array in descending order; pass function descending   // as an argument to specify descending sorting order   else    {      selectionSort( a, arraySize, descending );      cout << "\nData items in descending order\n";   } // end else part of if...else   // output sorted array   for ( counter = 0; counter < arraySize; counter++ )      cout << setw( 4 ) << a[ counter ];   cout << endl;} // end main// multipurpose selection sort; the parameter compare is a pointer to// the comparison function that determines the sorting ordervoid selectionSort( int work[], const int size,                    bool (*compare)( int, int ) ){   int smallestOrLargest; // index of smallest (or largest) element   // loop over size - 1 elements   for ( int i = 0; i < size - 1; i++ )   {      smallestOrLargest = i; // first index of remaining vector      // loop to find index of smallest (or largest) element      for ( int index = i + 1; index < size; index++ )         if ( !(*compare)( work[ smallestOrLargest ], work[ index ] ) )            smallestOrLargest = index;      swap( &work[ smallestOrLargest ], &work[ i ] );   } // end if} // end function selectionSort// swap values at memory locations to which // element1Ptr and element2Ptr pointvoid swap( int * const element1Ptr, int * const element2Ptr ){   int hold = *element1Ptr;   *element1Ptr = *element2Ptr;   *element2Ptr = hold;} // end function swap// determine whether element a is less than // element b for an ascending order sortbool ascending( int a, int b ){   return a < b; // returns true if a is less than b} // end function ascending// determine whether element a is greater than // element b for a descending order sortbool descending( int a, int b ){   return a > b; // returns true if a is greater than b} // end function descending

1. const
   （1） 对于const对象，不允许进行成员函数的调用，除非成员函数本身也声明为const。这一点非常严格，即使是不修改对象的获取对象函数也不行。
   （2）不为const数据成员提供相应地成员初始化器是一个编译错误。
2. Friend
   （1） 类的friend函数（友元函数）在类的作用域之外定义，却具有访问类的非public（以及public）成员的权限。单独的函数或整个类都已被声明为另一个类的友元。
   （2） 使用friend函数可以提高程序的性能。
   （3） 友元声明可以出现在类的任何地方。
3. 多种格式输出日期
   格式：
   DDD YYYY
   MM/DD/YYYY
   June 14, 1992
   Date.h

#ifndef DATE_H#define DATE_H#include <string>using namespace std;class Date {public:   Date(); // default constructor uses <ctime> functions to set date   Date( int, int ); // constructor using ddd yyyy format   Date( int, int, int ); // constructor using dd/mm/yy format   Date( string, int, int ); // constructor using Month dd, yyyy format   void setDay( int ); // set the day   void setMonth( int ); // set the month   void print() const; // print date in month/day/year format   void printDDDYYYY() const; // print date in ddd yyyy format   void printMMDDYY() const; // print date in mm/dd/yy format   void printMonthDDYYYY() const; // print date in Month dd, yyyy format   ~Date(); // provided to confirm destruction orderprivate:   int month; // 1-12 (January-December)   int day; // 1-31 based on month   int year; // any year   // utility functions    int checkDay( int ) const; // check if day is proper for month and year    int daysInMonth( int ) const; // returns number of days in given month   bool isLeapYear() const; // indicates whether date is in a leap year   int convertDDToDDD() const; // get 3-digit day based on month and day   void setMMDDFromDDD( int ); // set month and day based on 3-digit day   string convertMMToMonth( int ) const; // convert mm to month name   void setMMFromMonth( string ); // convert month name to mm    int convertYYYYToYY() const; // get 2-digit year based on 4-digit year   void setYYYYFromYY( int ); // set year based on 2-digit year}; // end class Date#endif

Date.cpp

#include <iostream>#include <iomanip>#include <ctime>#include "Date.h" // include Date class definitionusing namespace std;// default constructor that sets date using <ctime> functionsDate::Date(){   // pointer of type struct tm which holds calendar time components   struct tm *ptr;    time_t t = time( 0 ); // determine current calendar time         // convert current calendar time pointed to by t into   // broken down time and assign it to ptr   ptr = localtime( &t );    day = ptr->tm_mday; // broken down day of month   month = 1 + ptr->tm_mon; // broken down month since January   year = ptr->tm_year + 1900; // broken down year since 1900} // end Date constructor// constructor that takes date in ddd yyyy formatDate::Date( int ddd, int yyyy ){   year = yyyy; // could validate   setMMDDFromDDD( ddd ); // set month and day based on ddd} // end Date constructor// constructor that takes date in mm/dd/yy formatDate::Date( int mm, int dd, int yy ){   setYYYYFromYY( yy ); // set 4-digit year based on yy   setMonth( mm ); // validate and set the month   setDay( dd ); // validate and set the day} // end Date constructor// constructor that takes date in Month dd, yyyy formatDate::Date( string monthName, int dd, int yyyy ){    setMMFromMonth( monthName ); // set month based on month name   setDay( dd ); // validate and set the day   year = yyyy; // could validate} // end Date constructor// validate and store the dayvoid Date::setDay( int d ){   day = checkDay( d ); // validate the day} // end function setDay// validate and store the monthvoid Date::setMonth( int m ){   if ( m > 0 && m <= 12 ) // validate the month      month = m;   else    {                           month = 1; // invalid month set to 1      cout << "Invalid month (" << m << ") set to 1.\n";   } // end else} // end function setMonth// print Date object in form: month/day/yearvoid Date::print() const{   cout << month << '/' << day << '/' << year << endl; } // end function print// print Date object in form: ddd yyyyvoid Date::printDDDYYYY() const{   cout << convertDDToDDD() << ' ' << year << endl;} // end function printDDDYYYY// print Date object in form: mm/dd/yyvoid Date::printMMDDYY() const{   cout << setw( 2 ) << setfill( '0' ) << month << '/'       << setw( 2 ) << setfill( '0' ) << day << '/'       << setw( 2 ) << setfill( '0' ) << convertYYYYToYY() << endl;} // end function printMMDDYY// print Date object in form: Month dd, yyyyvoid Date::printMonthDDYYYY() const{   cout << convertMMToMonth( month ) << ' ' << day << ", " << year       << endl;} // end function printMonthDDYYYY// output Date object to show when its destructor is calledDate::~Date(){    cout << "Date object destructor for date ";   print();   cout << endl;} // end ~Date destructor// utility function to confirm proper day value based on // month and year; handles leap years, tooint Date::checkDay( int testDay ) const{   // determine whether testDay is valid for specified month   if ( testDay > 0 && testDay <= daysInMonth( month ) )      return testDay;   // February 29 check for leap year    if ( month == 2 && testDay == 29 && isLeapYear() )      return testDay;   cout << "Invalid day (" << testDay << ") set to 1.\n";   return 1; // leave object in consistent state if bad value} // end function checkDay// return the number of days in a monthint Date::daysInMonth( int m ) const{   if ( isLeapYear() && m == 2 )      return 29;   static const int daysPerMonth[ 13 ] =       { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };   return daysPerMonth[ m ];} // end function daysInMonth// test for a leap yearbool Date::isLeapYear() const{   if ( year % 400 == 0 || ( year % 4 == 0 && year % 100 != 0 ) )      return true;   else      return false;} // end function isLeapYear// calculate 3-digit day based on Date object's current month and dayint Date::convertDDToDDD() const{   int ddd = 0;   // for each month that has passed, add days to ddd   for ( int i = 1; i < month; i++ )      ddd += daysInMonth( i );   // add days from current month   ddd += day;   return ddd;} // end function convertDDToDDD// set month and day based on 3-digit dayvoid Date::setMMDDFromDDD( int ddd ){   int dayTotal = 0;   int m;   for ( m = 1; m <= 12 && ( dayTotal + daysInMonth( m ) ) < ddd; m++ )      dayTotal += daysInMonth( m );   setMonth( m );   setDay( ddd - dayTotal );} // end function setMMDDFromDDD// utility function to convert month number to month namestring Date::convertMMToMonth( int mm ) const{   static const string months[] =       { "", "January", "February", "March", "April", "May", "June",       "July", "August", "September", "October", "November", "December" };   return months[ mm ];} // end function convertMMToMonth// set month number based on month name    void Date::setMMFromMonth( string m ){   bool matchFound = false;   // loop for each month, checking for a match   for ( int i = 1; i <= 12 && !matchFound; i++ )   {      string tempMonth = convertMMToMonth( i );      if ( tempMonth == m )      {         setMonth( i );         matchFound = true;      } // end if   } // end for   if ( !matchFound )   {      cout << "Invalid month name (" << month << "). month set to 1.\n";      setMonth( 1 ); // leave object in consistent state if bad value   } // end if} // end function setMMFromMonth// utility function to convert 4-digit year to 2-digit yearint Date::convertYYYYToYY() const{   // if year is in 2000s, subtract 2000   // else, assume year is in the 1900s and subtract 1900   return ( year >= 2000 ? year - 2000 : year - 1900 );} // end function convertYYYYtoYY// utility function to convert 2-digit year to 4-digit yearvoid Date::setYYYYFromYY( int yy ){   // if yy is less than 7, assume it is in the 2000s   // if yy is greater than or equal to 7, assume it's in the 1900s   year = ( yy < 7 ? yy + 2000 : yy + 1900 );} // end function setYYYYFromYY

Main

#include <iostream> #include "Date.h" // include Date class definitionusing namespace std;int main(){   Date date1( 256, 1999 ); // initialize using ddd yyyy format   Date date2( 3, 25, 04 ); // initialize using mm/dd/yy format   Date date3( "September", 1, 2000 ); // "month" dd, yyyy format   Date date4; // initialize to current date with default constructor   // print Date objects in default format   date1.print();   date2.print();   date3.print();   date4.print();   cout << '\n';   // print Date objects in 'ddd yyyy' format   date1.printDDDYYYY();    date2.printDDDYYYY();   date3.printDDDYYYY();   date4.printDDDYYYY();   cout << '\n';   // print Date objects in 'mm/dd/yy' format   date1.printMMDDYY();    date2.printMMDDYY();   date3.printMMDDYY();   date4.printMMDDYY();   cout << '\n';   // print Date objects in '"month" d, yyyy' format   date1.printMonthDDYYYY();   date2.printMonthDDYYYY();   date3.printMonthDDYYYY();   date4.printMonthDDYYYY();   cout << endl;} // end main