Java邏輯錯誤與基礎數學

Question

我正在通過一個基本的java課程，並且有一個非常困難的時間思考編程式的盟友，所以我忍受着這裏。我應該編寫一個程序，在用戶定義的範圍內總結所有的奇數 - 簡單的權利？嗯，我認爲我的代碼已經算出來了，但數學總是出錯。代替1到14等於19（1 + 3 + 5 ...）的範圍，程序返回46.它只有3，所以我覺得我正在接近正確的代碼。

下面是電流輸出樣本：

The value input is 14 
DEBUG: The current value of variable sum is: 4 
DEBUG: The current value of variable ctr is: 3 
DEBUG: The current value of variable sum is: 10 
DEBUG: The current value of variable ctr is: 7 
DEBUG: The current value of variable sum is: 22 
DEBUG: The current value of variable ctr is: 11 
DEBUG: The current value of variable sum is: 46 
DEBUG: The current value of variable ctr is: 15 
The sum of the odd numbers from 1 to 14 is 46 

這裏的麻煩的方法：

public static void calcSumPrint(int topEndNumber) { 
    //calc and print sum of the odd number from 1 to top-end number 
    //uses loop to add odd numbers 
    //display results: range (eg: 1 to 13), sum of odd numbers 
     for (ctr = 1; ctr <= topEndNumber; ctr = ctr + 2) { 
      nextOddNumber = sum + 2; 
      sum = sum + nextOddNumber; 
      ctr = ctr + 2; 
      if (debug) { 
       System.out.println("DEBUG: The current value of variable sum is: " + sum); 
       System.out.println("DEBUG: The current value of variable ctr is: " + ctr); 
      } 
     } 

     System.out.println("The sum of the odd numbers from 1 to " + topEndNumber + " is " + sum); 

    }//end of calcSumPrint 

這裏的程序：

import java.util.Scanner; 

public class sumOdds { 
    static int topEndNumber = 0; 
    static int ctr = 0; 
    static int intermediateSum = 0; 
    static int sum = 1; 
    static boolean debug = true; 
    static int nextOddNumber = 0; 


    public static void main(String[] args) { 
     getLimitNumber(); 
     System.out.println("The value input is " + topEndNumber); 
     calcSumPrint(topEndNumber); 

    }//end of main 

    public static int getLimitNumber() { 
     //lets uer input top-end number to be used in program [X] 
     //catches exception if non-integer value is used [X] 
     //verifies that the input number has a value of at least 1 [ ] 
     //returns verified int to method caller [ ] 
     Scanner input = new Scanner(System.in); 
     boolean done = false; 
     while (done != true) { 
      try { 
       System.out.println("Enter a positive whole top-end number to sum odds of:"); 
       topEndNumber = input.nextInt(); 
        if (topEndNumber <= 0){ 
         throw new NumberFormatException(); 
        } 
       done = true; 
      }//end of try 
      catch (Exception message) { 
       //put exception in here 
       input.nextLine(); 
       System.out.println("Bad input, retry"); 
      }//end of catch 
     }//end of while 
     input.close(); 


     //to shut up eclipse 
     return topEndNumber; 


    }//end of getLimitNumber 

    public static void calcSumPrint(int topEndNumber) { 
    //calc and print sum of the odd number from 1 to top-end number 
    //uses loop to add odd numbers 
    //display results: range (eg: 1 to 13), sum of odd numbers 
     for (ctr = 1; ctr <= topEndNumber; ctr = ctr + 2) { 
      nextOddNumber = sum + 2; 
      sum = sum + nextOddNumber; 
      ctr = ctr + 2; 
      if (debug) { 
       System.out.println("DEBUG: The current value of variable sum is: " + sum); 
       System.out.println("DEBUG: The current value of variable ctr is: " + ctr); 
      } 
     } 

     System.out.println("The sum of the odd numbers from 1 to " + topEndNumber + " is " + sum); 

    }//end of calcSumPrint 

    public static int doAgain() { 
    //ask and verify the user wants to re-run program, return int 

    //to shut up eclipse 
     return 20000; 
    }//end of doAgain 

}//end of class 

做任何事情在你跳出來，我可能是失蹤？我很想知道這個問題，並且一直在辦公室裏對算法進行可視化處理，結果導致數學無法解決。

Answer 1

在你for循環CTR的值已經由兩個

增加，以致

sum = 0; 
for (ctr = 1; ctr <= topEndNumber; ctr = ctr + 2) { 
     sum += ctr; 
} 

會給你所需要的答案。