while循環重複兩次，不遵循條件

Question

我是Java新手，遇到了一些問題。我的教師要求我在while循環中嵌套do while循環; do while循環會爲中期，最終和項目等級的用戶可輸入的等級類型（大於0但小於100）創建限制。然後將此輸入用於計算這三個等級的平均值。

但是，我的while while循環運行了兩次，並使用來自計算中第二個提示的輸入的平均值。我究竟做錯了什麼？我已經瀏覽了我的教科書和這個網站，但我似乎無法理解爲什麼它這樣做，因爲它只提示兩次，然後只使用第二個提示的輸入。任何幫助將不勝感激。感謝您花時間閱讀我的文章！

爲了清楚起見，這裏是我的代碼：

System.out.println("******** Step 2: Grading for Multiple Students *********"); 
    System.out.println(); 
    // Create scanner object for text and number 
    Scanner textReader = new Scanner(System.in); 
    Scanner numberReader = new Scanner(System.in); 
    System.out.print("Would you like to input grades (y/n): "); 
    String response = textReader.nextLine(); 
    // Create while loop for first yes/no question 
    while ((!response.equalsIgnoreCase("y")) && (!response.equalsIgnoreCase("n"))) 
    { 
     System.out.print("y/n needed: "); 
     response = textReader.nextLine(); 
     System.out.println(); 
    } 
    while ((response.equalsIgnoreCase("y"))) 
    { 
     System.out.print("\nStudent Name: "); 
     String studentName = textReader.nextLine(); 
     System.out.print("Course Name: "); 
     String courseName = textReader.nextLine(); 
     System.out.print("Midterm Grade (needs to be between 0-100): "); 
     double midtermGrade = numberReader.nextDouble(); 
     do 
     { 
      System.out.print("Midterm Grade (needs to be between 0-100): "); 
      midtermGrade = numberReader.nextDouble(); 
      break; 
     } 
     while ((midtermGrade < 0) || (midtermGrade > 100)); 
     System.out.print("Final Grade (needs to be between 0-100): "); 
     double finalGrade = numberReader.nextDouble(); 
     do 
     { 
      System.out.print("Final Grade (needs to be between 0-100): "); 
      finalGrade = numberReader.nextDouble(); 
     } 
     while ((finalGrade < 0) || (finalGrade > 100)); 
     System.out.print("Project Grade (needs to be between 0-100): "); 
     double projectGrade = numberReader.nextDouble(); 
     do 
     { 
      System.out.print("Project Grade (needs to be between 0-100): "); 
      projectGrade = numberReader.nextDouble(); 
     } 
     while ((projectGrade < 0) || (projectGrade > 100)); 

這裏是我的輸出：

Output link

Answer 1

在do-while循環，該循環稱爲至少一次，無論的條件。 在正常的while循環中，只有滿足條件時纔會調用循環。

代替

System.out.print("Final Grade (needs to be between 0-100): "); // remove this 
double finalGrade = numberReader.nextDouble(); // remove this 
do 
{ 
    System.out.print("Final Grade (needs to be between 0-100): "); 
    finalGrade = numberReader.nextDouble(); 
} 
while ((finalGrade < 0) || (finalGrade > 100)); 

只需刪除上述片斷的前兩行的每個輸入迴路。