Java的基本循環

Question

我不知道爲什麼我的第二個for循環將不執行。它編譯，但是當我運行這個它不起作用〜_〜

import java.util.Scanner; 

public class ranges 
{ 


public static void main (String[] args) 

    { 

Scanner scan = new Scanner (System.in); 

     int size; 
     int input; 
     int count = 0; 
     int occurence = 0; 
     System.out.print ("Please enter the size of your array: "); 
     size = scan.nextInt(); 
     int[] list = new int[size]; 



     for (int index = 0 ; index < list.length ; index++) 
     { 
      System.out.print ("Please enter an integer between 0 to 50: "); 
      input = scan.nextInt(); 

      if (input >= 0 && input <= 50) 
      { 
       list[index] = input; 
      } 
      else 
      { 
       System.out.println ("Invalid output, please try again"); 
       index--; 
      } 
     } 




     int right = (list.length)-1; 
     int left = 0; 

     for (int counter = left ; counter < list.length ; counter++) 
     { 
      while (right >= left) 
      { 
       if (list[left] == list[right]) 
       { 
        occurence++; 
        right--; 
       } 
      } 
      right = (list.length)-1; 
      System.out.println ("The number " + list[left] + " was added " + occurence + "4 times"); 
     } 

     for (int value : list) 
     { 
      System.out.print (value + " "); 
     } 
     ; 








    } 
} 

我更新的循環來evaulate OCCURENCES

對（INT左= 0;左< list.length;左++）

{

 while (right >= left) 
     { 
      if (list[left] == list[right]) 
      { 
       occurence++; 

      } 
      right--; 
     } 


     System.out.println ("The number " + list[left] + " was added " + occurence + " times"); 
     right = (list.length)-1; 
     occurence = 0; 
    } 

我已經洗乾淨了一下，現在出現次數是相同的輸入

Answer 1

你第二for也在努力。問題在於while環路條件，即while (right >= left)。如果list[left] == list[right]不相等，則會進入無限循環，因爲在這種情況下會更改right或left。

我想，你需要如下更改while（移動right--的if條件外）：

while (right >= left) 
    { 
    if (list[left] == list[right]) 
     { 
     occurence++; 
     } 
     right--; 
    } 

另外兩個問題：

請while循環之前重新初始化occurence =0;以便它計算每個數字的出現次數，並從您的System.out.println()中刪除4如下：

for (int counter = left ; counter < list.length ; counter++) 
{ 
    occurence = 0; //< initialize to 0 
    while (right >= left) 
    { 
     if (list[left] == list[right]) 
     { 
     occurence++; 
     } 
      right--; 
    } 
    right = (list.length)-1; 
     //remove 4 after "occurance +" 
    System.out.println ("The number " + list[left] + 
              " was added " + occurence + " times"); 
} 

編輯：

 Map<Integer, Integer> scannedNums = new HashMap<Integer, Integer>(); 
     for (int counter = left ; counter < list.length ; counter++) 
     { 
      if(scannedNums.get(list[counter]) == null){ 
       scannedNums.put(list[counter], 1); 
      }else{ 
       int currentCount = scannedNums.get(list[counter]); 
       scannedNums.put(list[counter], currentCount+1); 
      } 
     } 

     Set<Integer> nums = scannedNums.keySet(); 
     Iterator<Integer> numIter = nums.iterator(); 
     while(numIter.hasNext()){ 
      int number = numIter.next(); 
      System.out.println ("The number " + number + 
        " was added " + scannedNums.get(number) + " times"); 
     } 

Answer 2

只需快速瀏覽一下，並建議未來。

此代碼：

while (right >= left) 
    { 
     if (list[left] == list[right]) 
     { 
      occurence++; 
      right--; 
     } 
    } 

表明，如果列表[左] =列表[右]，但正確的依然是> =左側，這個循環將永遠不會停止！如果你想要的只是發現了多少次事件的計數，你可能想要將if語句的右側移動。

最後，當你說「循環不起作用」時，這有點幫助不大。也許顯示你的輸出，或者它不工作的方式會更好。

Answer 3

它給了什麼錯誤？

我看到的一個直接問題是，如果沒有發生，while循環將永遠運行。第一個for循環可能會使索引超出範圍。

對於第一個循環，而不是：

for (int index = 0 ; index < list.length ; index++) 
    { 
     System.out.print ("Please enter an integer between 0 to 50: "); 
     input = scan.nextInt(); 

     if (input >= 0 && input <= 50) 
     { 
      list[index] = input; 
     } 
     else 
     { 
      System.out.println ("Invalid output, please try again"); 
      index--; 
     } 
    } 

我會做：

for (int index = 0 ; index < list.length ; ++index) 
    { 
     while(true) 
     { 
      System.out.print ("Please enter an integer between 0 to 50: "); 
      input = scan.nextInt(); 
      if (input >= 0 && input <= 50) 
      { 
       list[index] = input; 
       break; 
      } 
      System.out.println ("Invalid output, please try again"); 
     } 
    } 

而對於第二個循環：

for (int counter = left ; counter < list.length ; counter++) 
    { 
     occurence = 0; 
     for(int i = counter; i <= right; ++i) 
     { 
      if(list[left] == list[i]) 
       ++occurence; 
     } 
     System.out.println ("The number " + list[left] + " was added " + occurence + " times"); 
    }