循環輸入和語句的列表

Question

循環這些語句的任何幫助。我對此很陌生，而且遇到了一些麻煩。我正在努力做到這一點，以便在給予班級平均分數之前，成績簿將五個孩子的成績。只需要幫助循環。

import java.util.Scanner; 
public class gradebook { 

    /** 
    * @param args 
    */ 
    public static void main(String[] args) { 
     // TODO Auto-generated method stub 

     float discussionweight, hwweight, examweight, discussion, hw, exam, finalaverage, again; 
     Scanner scan = new Scanner(System.in); 
     System.out.print("Enter the students name: "); 
     String student = scan.next(); 

     System.out.print ("Enter the weight of the discussions as an integer: "); 
     discussionweight = scan.nextFloat(); 

     // Prompts for the discussions grade 
     System.out.print ("Enter the score of the discussion as an integer: "); 
     discussion = scan.nextFloat(); 

     // Prompts for the weight of the homework grade in an integer 
     System.out.print ("Enter the weight of the homework as an integer: "); 
     hwweight = scan.nextFloat(); 

     // Prompts for hw grade 
     System.out.print ("Enter the hw grade: "); 
     hw = scan.nextFloat(); 

     System.out.print("Enter the weight of the exam as an integer"); 
     examweight = scan.nextFloat(); 

     System.out.print("Enter the exam grade"); 
     exam = scan.nextFloat(); 




     // Calculate and print the final, weighted average. 
     finalaverage = (((discussionweight * discussion) + (hw * hwweight) + (exam * examweight))/100); 

     if (finalaverage >= 90) 
     System.out.println(student +"'s " + "final grade is an A."); 
     else if (finalaverage >= 80) 
     System.out.println(student +"'s " + "final grade is a B."); 
     else if (finalaverage >= 70) 
     System.out.println(student +"'s " + "final grade is a C."); 
     else if (finalaverage >= 60) 
     System.out.println(student +"'s " + "final grade is a D."); 
     else if (finalaverage >= 10) 
     System.out.println(student +"'s " + "final grade is an F."); 


     System.out.println ("The final average is "+ finalaverage); 
     System.out.println ("Would you like to continue? Enter 0 to exit and anything else to continue."); 
     String again = scan.nextFloat(); 

     while (again != 0) { 
      finalaverage += again; 
     } 



    } 

Answer 1

做這種方式 當你想繼續一次又一次，你需要循環，直到出境成爲真正的條件下使用的邏輯。在這種情況下，循環將繼續執行，直到用戶輸入爲0，然後程序退出。

while(true) { 
    Scanner scan = new Scanner(System.in); 
    System.out.println("Enter the students name: "); 
    String student = scan.nextLine();//change to nextLine() 
    // rest all same 
    System.out.println("The final average is " + finalaverage); 
    System.out.println("Would you like to continue? Enter 0 to exit 
            and anything else to continue."); 
    again = scan.nextFloat(); 
    if(again == 0)// if input is zero it will continue or else it will exit 
     break; 
} 

改變這個String again = scan.nextFloat();到again = scan.nextFloat(); 因爲你已經通過名稱的變量再次float類型此外nextFloat（）爲您提供了float類型的輸入，然後你爲什麼需要在這種情況下字符串。

Answer 2

你不能在Java中重新聲明一個與你之前聲明的同名的變量。在你的程序String again = scan.nextFloat();你試圖做到這一點。而且你正在嘗試給一個不允許的字符串變量賦值一個浮點值。關於循環的問題，您可以使用一個簡單的while（..）循環，如下面的代碼所示，以繼續處理另一個學生數據。我不確定你是否需要finalaverage+= again;。請檢查一下。

import java.util.Scanner; 


public class gradebook { 

    /** 
    * @param args 
    */ 
    public static void main(String[] args) { 
     // TODO Auto-generated method stub 
     float discussionweight, hwweight, examweight, discussion, hw, exam, finalaverage, again ; 

     do { 

      Scanner scan = new Scanner(System.in); 
      System.out.print("Enter the students name: "); 
      String student = scan.next(); 

      ....// same as your code. 

      System.out.println ("The final average is "+ finalaverage); 
      System.out.println ("Would you like to continue? Enter 0 to exit and anything else to continue."); 
      again = scan.nextFloat(); 


      finalaverage += again; 
     } while (again != 0); 

    } 
} 

Answer 3

按照Java文檔

while語句而 特定條件爲真連續執行語句塊。其語法可以被表示爲：

而（表達式）{

statement(s) 

}

while語句計算表達式，其必須返回一個布爾 值。如果表達式的計算結果爲true，則while語句 將執行while代碼塊中的語句。 while語句 繼續測試表達式並執行其塊，直到 表達式計算結果爲false。

考慮所有計算邏輯，並將用戶輸入作爲statement(s)在上面的示例中。 while循環將執行，只要expression返回true布爾值。因此，您可以添加again!=0作爲expression，因爲當用戶按下0程序應該被終止。

變量也應該初始化爲非零值，以便第一次滿足條件。否則，您必須使用do-while循環。

scan.nextFloat（）將用戶輸入視爲浮點數。僅當用戶輸入爲浮動時才使用它。如果你聲明again爲int，那麼你必須使用scan.nextInt（）;

public class gradebook { 


/** 
* @param args 
*/ 
public static void main(String[] args) { 
    // TODO Auto-generated method stub 

    float discussionweight, hwweight, examweight, discussion, hw, exam, finalaverage; 
    int again=-1; 

    while(again!=0){ 

    Scanner scan = new Scanner(System.in); 
    System.out.print("Enter the students name: "); 
    String student = scan.next(); 

    System.out.print ("Enter the weight of the discussions as an integer: "); 
    discussionweight = scan.nextFloat(); 

    // Prompts for the discussions grade 
    System.out.print ("Enter the score of the discussion as an integer: "); 
    discussion = scan.nextFloat(); 

    // Prompts for the weight of the homework grade in an integer 
    System.out.print ("Enter the weight of the homework as an integer: "); 
    hwweight = scan.nextFloat(); 

    // Prompts for hw grade 
    System.out.print ("Enter the hw grade: "); 
    hw = scan.nextFloat(); 

    System.out.print("Enter the weight of the exam as an integer"); 
    examweight = scan.nextFloat(); 

    System.out.print("Enter the exam grade"); 
    exam = scan.nextFloat(); 




    // Calculate and print the final, weighted average. 
    finalaverage = (((discussionweight * discussion) + (hw * hwweight) + (exam * examweight))/100); 

    if (finalaverage >= 90) 
    System.out.println(student +"'s " + "final grade is an A."); 
    else if (finalaverage >= 80) 
    System.out.println(student +"'s " + "final grade is a B."); 
    else if (finalaverage >= 70) 
    System.out.println(student +"'s " + "final grade is a C."); 
    else if (finalaverage >= 60) 
    System.out.println(student +"'s " + "final grade is a D."); 
    else if (finalaverage >= 10) 
    System.out.println(student +"'s " + "final grade is an F."); 


    System.out.println ("The final average is "+ finalaverage); 
    System.out.println ("Would you like to continue? Enter 0 to exit and anything else to continue."); 
    again = scan.nextInt(); 


    } 
} 

Answer 4

讓我們分解一下需要發生的事情。

讓N是學生5的數量，

• 收集最終成績的學生
  • 收集作業的分數
  • 平均得分一起
• 重複直到你有N學生的成績
• 讓average是學生的成績平均

---

打破了這個問題分解成更小的部分。考慮「讓average成爲學生成績的平均值」。我們所知道的是：

• A級是float，所以我們需要一個方法（或「小部分」，正如我前面把它稱爲），將平均float值。

在Java中，你會表達這樣的方法是這樣的：

static float average(List<Float> terms) { 
    float total = 0;  // Begin with a total 0 - any summation begins here 
    for (float t : terms) { // For every float t in terms 
     total += t;   // add t to the total 
    } 
    return total/terms.size(); // return total divided by the number of terms 
} 

，然後進行測試，並確保這樣做你想要的位置：

public static void main(String[] args) { 
    // `test` is now a list of floats, we would expect average to be 
    // effectively equal to 2.5 
    List<Float> test = new ArrayList<>(Arrays.asList(2.0f, 2.5f, 3.0f)); 
    float actual = average(test); // This calls the average method above 
    System.out.println(actual); // and outputs to console, which prints 2.5 
} 

---

如何是一種平均的方法，它是測試，以確保它做你期望對你有用嗎？那麼，舉個例子，你現在有辦法收集一個float值的列表（使用List<Float>）。所以我們現在可以更詳細地表達上面的細節。

• 聲明List<Float>，如List<Float> grades = new ArrayList<Float>。
• 收集了學生的最終成績，由
  • 收集的分配的分數，然後
  • 平均得分在一起，（提示：也許你需要另一種不同average()方法來處理加權平均）
  • 和平均，存儲在grades例如grades.add(average)
• 重複，直到你有N學生的成績
• 使用平均得到最終的輸出，像float classAverage = average(grades)

一切有關規劃即將打破問題成其組成成分，然後進一步將它們分解，直到你reasonbly大小（閱讀：小）問題這可以簡單地解決，然後放到一個更大的程序中。

List<E> Documentation

ArrayList<E> Documentation