使用文件爲學生排隊 - 課堂作業

Question

這是我的CS1337類，所以我需要在主函數內工作。我不能使用任何東西，除了循環，if/else和switch語句。

我在記事本中創建了一個Lines.txt文件，該文件應該有一個需要讀取的名稱列表。最終結果應該是讀取所有名稱並在控制檯輸出中顯示一條消息。

我根據我的代碼關閉前一個條目我在網上找到的位置： Question about my design for my C++ homework

任何幫助將不勝感激。

Lines.txt

Leslie 
Ron 
Tom 
Gerry 
Donna 
Andy 
April 
Chris 
Ben 
Mark 

控制檯窗口輸出：

Andy should be at the head of the line. 
Tom should be at the end of the line. 

我的代碼：

int main() 
{ 
    ifstream inputFile; 
    string filename; 

    string front, back, student; 
    int students = 10; 

    // Get the filename from the user. 
    cout << "Enter the filename: "; 
    cin >> filename; 

    // Open the file. 
    inputFile.open(filename.c_str()); 

    // If the file successfully opened, process it. 
    if (inputFile) 
    { 
/* A formula the sets each name entered to 
the variables front and back*/ 

    front = back = student; 

    // Read the numbers from the file and 
    // display them. 

    while (inputFile >> student) 
    { 
    for (int count = 1; count <= students; ++count) 
    { 
     // Create an if/else statement that decides which 
     // student name is alphabetically first and last 

    if (student < front) 
     front = student; 
    else if (student >= back) 
     back = student; 
    } 
    // Display the message showing which name is alphabetically first and last name 
    } 
    cout << endl 
     << front << " should be at the head of the line." << endl 
      << back << " should be at the end of the line." << endl; 
    // Close the file. 
    inputFile.close(); 
} 
    else 
{ 
    // Display an error message. 
    cout << "Error opening the file.\n"; 
} 
return 0; 
} 

Answer 1

不是一個糟糕的開局。主要的問題是這樣的：

if (student < front) 

第一次遇到這種運行，front是一個空字符串...什麼都比較小於空字符串。也許最簡單的解決方法是：

if (count == 1) 
    front = back = student; 
else if (student < front) 
    ...etc... 

小挑剔：

• 你的第一個front = back = student;什麼也不做......所有的字符串是缺省構造是空的反正。

• 嘗試創建和初始化的變量越晚越好，例如... if (std::ifstream inputFile(filename) { ... } else { ...couldn't open... } - 無需.close()召喚爲std::ifstream將從其析構函數關閉文件。在C++ 11之前，您只需要.c_str()。