Java-如何使用while循环解决此计算

我对过去试卷上的一道题有困难。我正在尝试将一个

从

数字乘以一个

n

数字。换句话说：from*（from+1）（from+2）.*n

我需要使用while循环来解决这个问题。到目前为止，我已经这样做了，不知道该怎么办。我知道代码是错的，但已经被卡住了一段时间

public class Fact {

    public int last;

    private int factPartND(final int from, final int n) {
        int fromNum = from;
        int toNum = n;
        int result = 1;
        int c = 1;

        while (fromNum <= toNum) {  // e.g.5*6*7*8*9*10*11
            result = (fromNum) * (fromNum + c);  // calculate 5*6
            final int temp = result;  // store 5*6
            int result1 = temp * (fromNum + c);  // store 5*6*7*....
            c++;  // increments the fromNum in the while code
            fromNum++;  // increments 5 to 11 in the while condition
            last = result1;
        }
        return last;
    }

    public static void main(String[] args) {
        Fact f = new Fact();
        System.out.println(test);
    }
}

公共类事实{
公共int最后；
私有内部资料部分ND（最终内部资料来源，最终内部资料n）{
int fromNum=from；
int toNum=n；
int结果=1；
int c=1；
while（fromNum我认为这应该作为while循环工作

int offset = 0;
int result = fromNum;
while (offset < toNum - fromNum) {
  offset++;
  result *= fromNum+offset;
}

int offset=0；
int结果=fromNum；
while（偏移量
一些伪代码：

result = from;
temp = from+1;
while(temp <= n) {
  result*=temp;
  temp++;
}

result=from；
温度=从+1开始；
而（温度
intc=0；
int结果=fromNum；
while（（fromNum+c）

快速尝试。希望有帮助：-）
我将尝试更广泛地回答这个问题，而不仅仅是在
循环时专注于
。请注意注释：

public class Fact {//I assume, based on your question, you really mean 'Factorial'.
    //Examining this for the first time I might assume that this object has to do with 
    //well-established observations, or 'Facts'. Fight the urge to abbreviate everything.

    public int last;//Why is this a member variable of the class?

    private int factPartND(final int from, final int n) {
        //How are your 'from' and 'n' variables related? It's unclear based on their names.
        //The method name is also incomprehensible.
        //Why are the parameters declared 'final'?
        //Why is this a private method?
        //Why is this not a static method?

        int fromNum = from;//If you're redeclaring, there is probably a problem.
        int toNum = n;
        int result = 1;//Is this your default result? You should be notating it in the method
            //comments if you're assuming some things, like no negative numbers.
        int c = 1;//What is c?


        //You have latched on to 'while' as the only way of doing this.
        while (fromNum <= toNum) {  // e.g.5*6*7*8*9*10*11
            result = (fromNum) * (fromNum + c);  // calculate 5*6
               //And then set result to the result? What about what was in there before?
            final int temp = result;  // store 5*6
               //Why is this int final?
            int result1 = temp * (fromNum + c);  // store 5*6*7*....
            c++;  // increments the fromNum in the while code
               //Actually increments the adder to what you're multiplying by three lines earlier
            fromNum++;  // increments 5 to 11 in the while condition
            last = result1;
               //Your use of temporary variables is way overdone and confusing.
        }
        return last;
    }

    public static void main(String[] args) {
        Fact f = new Fact();
        System.out.println(test);
    }
}

请注意，此解决方案基本上有三行。它利用了您的问题分解为一个稍小的问题这一事实。它还优雅地处理您的边缘情况（以及对预期结果的评论）

同样要注意的是，这种方法（一种“递归”方法）会对性能产生影响，但过早优化是万恶之源，正如您第一次尝试时存在清晰度问题一样。
这里是您的中心方法的一个简单版本：

private int factPartND(final int from, final int n) {
    int f = from;
    int result = 1;

    while (f <= n) {
        result *= f++;
    }
    return result;
}

简单！
你看起来太复杂了。先弄清楚你在纸上是怎么做的，然后编写代码。简单化。我一开始试过了，但我找不到不乘以初始fromNum的方法，因为我在每次迭代中都不断乘以该数字。@ColinD，不，这是过去一篇论文中的问题，我有一个是soon@Colin问题上说这是一张旧试卷？所以不是homework@MattiLyra我以前做过家庭作业，包括修正考试中不正确的问题：p。只是要求确保。这不使用
而
loop@ColinD确实没有。@nsc010你真的需要在使用
的同时使用
吗？一个奇怪的要求。@MarkoTopolnik这是一个考试练习。这些都是这样的。顺便说一句，我不认为把它简化成一行对初学者来说是一个好例子。Java代码标准只是一个惯例，但对我来说是一个非常有用的标准。我已经见过太多这样的自由导致的错误了。@Tom我猜你是ri没错。这对我来说是自动的。顺便说一句，我从来没有看到过这样的错误，或者至少没有比任何其他类型的错误更常见。@Tom实际上有一个emacs小调模式，它会使parens变灰：）但在检查语法时，您只需将光标放在打开的paren上，即可立即看到S-expr达到的程度。这非常非常简单，比检查Java语法容易得多。另外，使用
paredit
进行编辑就像是一个新世界。这目前是错误的。您的循环检查fromNum
是否
，但您从未递增
fromNum
。另外，
result*fromNum+c
=
（result*fromNum）+c
回答得很好。我正要在评论中提到重新声明+1@Nathaniel福特，谢谢你的评论。行：
private int factPartND（final int from，final int n）
问题的一部分是我必须使用while循环。但是，我对其余的代码负责。我将检查您的反馈，并尝试在将来的编码中实现它们。感谢您抽出时间发表评论。@nsc010没问题！不过，我建议，即使在学术环境中也要使用常量质疑问题；如果有人给你一个可笑的签名来实现，就大声说出来。如果一些明显的东西可能更好，为什么会这样？最糟糕的情况是他们让你按原样实现，但在所有情况下，人们都意识到你真的在考虑这个问题。@NathanielFord
final
params，至少实际上是final（可以标记为
final
，没有编译错误），实际上是一种广泛推荐的做法。@MarkoTopolnik不要误解我的意思；我不反对它们是final，但前提是它有意义。作者需要理解为什么会是这种情况；否则，您主要只是复制、粘贴和屏蔽该方法的功能。
int result = 1, i = from;
while (i <= to) result *= i++;
System.out.println("Result is " + result);

public class Fact {//I assume, based on your question, you really mean 'Factorial'.
    //Examining this for the first time I might assume that this object has to do with 
    //well-established observations, or 'Facts'. Fight the urge to abbreviate everything.

    public int last;//Why is this a member variable of the class?

    private int factPartND(final int from, final int n) {
        //How are your 'from' and 'n' variables related? It's unclear based on their names.
        //The method name is also incomprehensible.
        //Why are the parameters declared 'final'?
        //Why is this a private method?
        //Why is this not a static method?

        int fromNum = from;//If you're redeclaring, there is probably a problem.
        int toNum = n;
        int result = 1;//Is this your default result? You should be notating it in the method
            //comments if you're assuming some things, like no negative numbers.
        int c = 1;//What is c?


        //You have latched on to 'while' as the only way of doing this.
        while (fromNum <= toNum) {  // e.g.5*6*7*8*9*10*11
            result = (fromNum) * (fromNum + c);  // calculate 5*6
               //And then set result to the result? What about what was in there before?
            final int temp = result;  // store 5*6
               //Why is this int final?
            int result1 = temp * (fromNum + c);  // store 5*6*7*....
            c++;  // increments the fromNum in the while code
               //Actually increments the adder to what you're multiplying by three lines earlier
            fromNum++;  // increments 5 to 11 in the while condition
            last = result1;
               //Your use of temporary variables is way overdone and confusing.
        }
        return last;
    }

    public static void main(String[] args) {
        Fact f = new Fact();
        System.out.println(test);
    }
}

public class Factorial {

  /** 
   *  Calculates the product of a series of integers from 'start' to 'end'. 'start' must be
   *  less than or equal to 'end', or it will return 1.
   */ 
  public static factorialRange(int start, int end) {
    if (start > end) { return 1; }

    if (start = end) { return end; }

    return start * factorialRange(start + 1, end);
  }

}

private int factPartND(final int from, final int n) {
    int f = from;
    int result = 1;

    while (f <= n) {
        result *= f++;
    }
    return result;
}

private int factPartND(int from, final int n) {
    int result = 1;

    while (from <= n) {
        result *= from++;
    }
    return result;
}