C++排序和二進制搜索與數組問題

Question

我是一個初學者程序員，並有解決此問題的問題。該任務是要求使用此方法（greaterAlpha（）），但我不完全確定目的是什麼。有人可以幫助我解決這個問題，並解釋這種方法的用途嗎？

我應該修復以前的作業，從文件中讀取，然後用點打印名稱和數字。 **加載項是排序函數，它應該使用greaterAlpha（）方法按字母順序對姓氏進行排序。畢竟，它應該循環使用一個鍵來使用相同的greaterAlpha（）方法進行二分搜索。 （二進制搜索中的排序爲它的比較中使用，如果發現必須返回元素的下標，最後測試元素的下標負，如果不。）

#include <iostream> 
#include <iomanip> 
#include <fstream> 
#include <string> 
using namespace std; 
//********************************************************************* 
class PhoneNumber 
{ 
    private: 
     int areaCode, 
      prefix, 
      lineNumber; 
    public:        // the methods are public 
    void setNumber(int area, int pre, int num) 
    { 
     areaCode = area; 
     prefix = pre; 
     lineNumber = num; 
    } 
    int getAreaCode() const 
    { 
     return areaCode; 
    } 
    int getPrefix() const 
    { 
     return prefix; 
    } 
    int getLineNumber() const 
    { 
     return lineNumber; 
    } 
    istream& readPhone(istream&);   // input/output functions 
    ostream& printPhone(ostream&) const; 
}; 
//********************************************************************* 
// Returns istream& so it can be used to overload the >> operator later 
istream& PhoneNumber::readPhone(istream& fin) 
{ 
    return fin >> areaCode >> prefix >> lineNumber; 
} 
//********************************************************************* 
// Returns ostream& so it can be used to overload the << opeator later 
ostream& PhoneNumber::printPhone(ostream& fout) const 
{ 
    fout << setw(4) << areaCode << "-" << prefix << "-" << lineNumber; 
    return fout; 
} 
//********************************************************************* 
class PhoneEntry 
{ 
    private: 
     string lastName, 
       firstName; 
     PhoneNumber Number; 
    public: 
     void setNames(string last, string first) 
     { 
      lastName = last; 
      firstName= first; 
     } 
     string getLastName() 
     { 
      return lastName; 
     } 
     string getFirstName() 
     { 
      return firstName; 
     } 
     istream& readEntry(istream&); 
     ostream& writeDots(ostream&, int); 
     ostream& printEntry(ostream&); 
     bool greaterAlpha(PhoneEntry&) const; 
     void selectionSort(string, int); 
}; 
//********************************************************************* 
istream& PhoneEntry::readEntry(istream& fin) 
{ 
    fin >> lastName >> firstName; 
    Number.readPhone(fin); 
    return fin; 
} 
//********************************************************************* 
ostream& PhoneEntry::writeDots(ostream& fout, int length) 
{ 
    length = firstName.length(); 
    length += lastName.length(); 
    length += 2; 
    //This line is causing the issue but WHY? 

    if(length % 2 == 1) 
    { 
     fout << "."; 
    } 

    for(length; length <= 28; length++) 
    { 
     fout << " ."; 
     length++; 
    } 

    return fout; 
} 
//********************************************************************* 
ostream& PhoneEntry::printEntry(ostream& fout) 
{ 
    int length = 0; 

    fout << lastName << ", " << firstName; 
    writeDots(fout, length); 
    Number.printPhone(fout); 

    return fout; 
} 
//********************************************************************* 
bool PhoneEntry::greaterAlpha (PhoneEntry& x) const 
{ 
    bool flag; 

    if (lastName > x.lastName) 
     flag = true; 
    else if ((lastName == x.lastName) && (firstName > x.firstName)) 
     flag = true; 
    else 
     flag = false; 

    return flag; 
} 
//********************************************************************* 
void selectionSort(string name[], int elems) 
{ 
    int startScan, minIndex; 
    string strName; 
    for (startScan = 0; startScan < (elems - 1); startScan++) 
    { 
     minIndex = startScan; 
     strName = name[startScan]; 
     for(int index = startScan + 1; index < elems; index++) 
     { 
      if (name[index] < strName) 
      { 
       strName = name[index]; 
       minIndex = index; 
      } 
     } 
     name[minIndex] = name[startScan]; 
     name[startScan] = strName; 
    } 
} 
//********************************************************************* 
int main() 
{ 
    int count; 
    const int MAX_CAPACITY = 500; 
    PhoneEntry Entry[MAX_CAPACITY], 
       EntryIn; 
    bool flag = false; 

    ifstream dataIn("phonenum.txt"); 

    if(!dataIn) 
    { 
     perror("phonenum.txt"); 
     exit(1); 
    } 

    count = 0; 
    while (count < MAX_CAPACITY && EntryIn.readEntry(dataIn)) 
    { 
     Entry[count++] = EntryIn; 
    } 

    dataIn.close(); 

    if (count == MAX_CAPACITY) 
    { 
     cerr << "Reached maximum capacity of " << MAX_CAPACITY << ", can't read anymore Phone Entries currently." << endl; 
    } 

    //EntryIn.greaterAlpha(Entry); 
    selectionSort(Entry, count); 

    if (flag) 
    { 
     for (int i = 0; i < count; i++) 
     { 
      Entry[i].printEntry(cout) << endl; 
     } 
    } 
    else 
     cerr << "Error with sort!" << endl; 

    return 0; 
} 

我知道這是編碼可怕的是，這是教練如何想寫這個。任何援助或建設性的批評將非常感激。

Answer 1

你只是問什麼greaterAlpha方法？

如果是的話，你應該在哪裏，你曾經使用<的排序和搜索，即

void selectionSort(PhoneEntry[] entries, int elems) 
{ 
// ... 
      PhoneEntry entry = entries[startScan]; 
// ... 
      if (entry.greaterAlpha(entries[index])) 
//... 
} 

二進制搜索也是一個非常簡單的變化，如果你已經有了將其用於比較兩個PhoneEntry實例它與std::string s一起實施。

邊注：許多寧願凝結比較法

bool PhoneEntry::greaterAlpha (PhoneEntry& x) const 
{ 
    return lastName > x.lastName 
     || (lastName == x.lastName && firstName > x.firstName); 
}