更改循环内的`double`输出

Question

我想开始说我是新手。我正在尝试做一个for循环，让我看到不同的40码破折号时间转换为MPH。问题是，就是BEING显示输出：

5.96 40 Time is 13.727882855399633 Miles Per Hour 
6.96 40 Time is 11.755485893416928 Miles Per Hour 
7.96 40 Time is 10.27866605756053 Miles Per Hour 

我想让它显示为5.96，5.97，5.98，等等，而不是5.96和6.96。

有没有人明白我想要做什么以及解决我遇到的这个问题？

public class FortyToMPH { 

    public static void main (String args []) { 
     double yards, foot, FeetInMiles, SecondsPerHour,FeetLength; 
     double FortyTime, Minutes, SecondsPerMile, MPH; 
     int counter; 


     counter = 0; 

     for(FortyTime = 4.96; FortyTime <= 7.99; FortyTime++) { 
     yards = 40; // length in yards 
     foot = yards * 3; // convert to feet 
     System.out.println(); 

     FeetInMiles = 5280; // The number of feet in a Mile 
     SecondsPerHour = 3600; 

     FeetLength = FeetInMiles/foot; // You divide the Feet in Miles by the feet conversion of 40 yards 
     System.out.println(); 

     SecondsPerMile = FeetLength * FortyTime; 
     MPH = SecondsPerHour/SecondsPerMile; 
     System.out.println(FortyTime + " 40 Time is " + MPH + " Miles Per Hour "); 

     counter++; 
     // every 10th line, print a blank line 
     if(counter == 10) { 
      System.out.println(); 
      counter = 0; // reset the line counter 


     } 

     } 
    } 
} 

Answer 1

在这里，我改性你给打印兼作2个小数位数字（见格式％.2f）在回路中产生的同时（用于循环步骤在DELTA变量被定义）的代码。

public class FortyToMPH 
{ 
    public static void main (String args []) 
    { 
     double yards, foot, feetLength; 
     double fortyTime = 4.96, minutes, secondsPerMile, mph; 
     int counter = 0; 
     /** 
     * Constants. 
     */  
     final double FEET_IN_MILES = 5280; 
     final double SECONDS_PER_HOUR = 3600; 
     final double DELTA = 0.01; 
     final double END  = 7.99; 

     while (fortyTime <= END) 
     { 
      yards = 40; // length in yards 
      foot = yards * 3; // convert to feet 

      feetLength = FEET_IN_MILES/foot; // You divide the Feet in Miles by the feet conversion of 40 yards 

      secondsPerMile = feetLength * fortyTime; 
      mph = SECONDS_PER_HOUR/secondsPerMile; 
      System.out.format("%.2f 40 Time is %.2f Miles Per Hour%n", fortyTime, mph); 

      counter++; 
      // every 10th line, print a blank line 
      if(counter == 10) { 
       System.out.println(); 
       counter = 0; // reset the line counter 
      } 

      fortyTime += DELTA; 
     } 
    } 
} 

Answer 2

的问题是，您使用的++运营商在for循环定义：

for(FortyTime = 4.96; FortyTime <= 7.99; FortyTime++) { 

变化for循环while循环包括线由0.01每次循环递增FortyTime：

while(FortyTime <= 7.99) { 
    FortyTime += 0.01; 
    // execute the rest of your code here 
} 

MarounMaroun正确地指出，使用double作为循环计数器存在令人讨厌的浮点算术错误的风险，所以我已经将for循环更改为while循环。

运算符++表示“重新分配x的值为x + 1”。它只会给你增量（或递减，与--）为1.

请注意，这将打印出数百行之前完成。

Answer 3

只是改变for循环是这样的：

for(FortyTime = 4.96; FortyTime <= 7.99; FortyTime=FortyTime+.01) 

，并打印它像

System.out.println((float)FortyTime + " 40 Time is " + MPH + " Miles Per Hour "); 

Answer 4

你需要做出两个改变：

for(FortyTime = 4.96; FortyTime <= 7.99; FortyTime=FortyTime+0.01) 

从而使FortyTime递增0.01而不是1和

System.out.printf("%.2f 40 Time is %f Miles Per Hour ", FortyTime, MPH); 

因此它以正确的精度打印。

Answer 5

我会建议你使用你的循环int并执行循环内的double一切都计算，以防止问题与浮点运算：

for(int i = 0; i < something; i++) { 
    double fortyTime = 4.96 + i; 
    //... 
} 

也请注意Java Naming Conventions和重命名你的变量。

为了证明浮点运算的问题，试试这个循环：

for(double i = 0; i < 1.0; i += 0.1) 
    System.out.println(i); 

这将打印

0.0 
0.1 
0.2 
0.30000000000000004 
0.4 
0.5 
0.6 
0.7 
0.7999999999999999 
0.8999999999999999 
0.9999999999999999 

而且你不想在你的程序是这样的输出。