double | 易学教程

Odd behavior comparing doubles, two PHP double values aren't equivalent

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问题 I have two seemingly equal double values in PHP (at least when echoing them). But when comparing them with double equals, for some reason, it evaluates to false. Are there any special considerations when performing this kind of comparison? 回答1: You shouldn't compare floating point numbers using the == operator. See the big warning and explanation in the php manual What will work is asserting that the two numbers are within a certain small distance of each other like this: if(abs($a - $b) < 0

Odd behavior comparing doubles, two PHP double values aren't equivalent

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Quicksort with double* values

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问题 I am given a programme in C which implements Quicksort on arrays with int values. I need to convert it into a programme which will implement Quicksort on arrays with double* values. I thought that I just need to change "int" declarations into "double*", but for some reason the programme no longer works when I test arrays with other values than integers. Can someone please help? I really know almost nothing about programming in C and have no idea how to go on. Here is the "int" programme: void

C语言基础学习基本数据类型-浮点型

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float和double 加了小数点的数都是浮点数。C语言有两种书写浮点数的方式，一种是使用常用的标准小数点表示法，如下： 0.00056 8.0 1.23 第二种表示浮点值叫做 E表示法。下面是一些例子: 2.52e-8 1.32E9 //E表示法不区分大小写 7E5 9.11e-31 其中，2.52e-8指的是2.52除以10的8次方，7E5指的是7乘以10的5次方。也就是说，E（或e）后面是10的指数。当指数为负时，意味着除以10的乘方。printf()函数用%e说明符打印使用E表示法的数字。 C语言中浮点类型有 float、double和long double 类型。浮点数的取值范围比整数大的多，float类型必须至少能表示6位有效数字，double类型至少能表示10位有效数字。 float和double类型输出说明符为%f，%f的输出格式默认保留6位小数，如果你只想保留小数点后3位数，你可以使用%.3f的形式来输出。浮点变量的定义如下： float 变量名 = 值; double 变量名 = 值; 观察一下下面这段代码的输出吧： #include<stdio.h> int main(void) { //定义一个double类型的变量并初始化，变量名为score，然后使用printf语句输出你的变量值 //在这里写下你的代码 double score=1

Java: Why we need to cast a float but not a double?

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问题 I don't know if you consider this an important question or not but I want to know. float is a float number (4 bytes). double is a float number (8 bytes). Why we define double wihtout casting: double d = 2.1; But we need to cast with floats: float f = (float) 2.1; or float f = 2.1f; Thank you in advance. 回答1: A floating-point literal is of type float if it ends with the letter F or f ; otherwise its type is double and it can optionally end with the letter D or d . The floating point types (

Double array initialization in Java

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问题 I was reading a book on Java and came across an example in which an array of type double was initialized in a way that I haven't seen before. What type of initialization is it and where else can it be used? double m[][]={ {0*0,1*0,2*0,3*0}, {0*1,1*1,2*1,3*1}, {0*2,1*2,2*2,3*2}, {0*3,1*3,2*3,3*3} }; 回答1: This is array initializer syntax , and it can only be used on the right-hand-side when declaring a variable of array type. Example: int[] x = {1,2,3,4}; String y = {"a","b","c"}; If you're not

Trying to draw lines based on doubles but nothing shows?

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问题 Here's the class in which I try to draw the lines package gps; import java.awt.*; import java.awt.geom.Line2D; import java.util.*; import javax.swing.*; public class RoadMap extends JPanel { public void paintComponent(Graphics2D g) { super.paintComponent(g); g.setColor(Color.blue); for(int i = 0; i < Graph.getEdges().length; i++) { Shape s = new Line2D.Double(Graph.vMap.get(Graph.getEdges()[i].i1).x, Graph.vMap.get(Graph.getEdges()[i].i1).y, Graph.vMap.get(Graph.getEdges()[i].i2).x, Graph

counting float digits (hw) C

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问题 I need to count digits from a float number and keep the number. I can use scanf() with %f or %c but not %s , and I can use getchar() . I can use getchar but I will loose the number. 回答1: Why will you lose the number with getchar ? Read characters with getchar until you hit whitespace/enter/end of input Collect them all into a single string Use strtod to make sure it's a valid floating point value Count digits in the string - either before, or after the point, whatever you need. If you're

单例模式的3种实现方式, 及其性能对比

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1. 懒汉模式(double check), 线程安全, 效率不高, 可以延迟加载 public class Singleton1 implements Serializable { // 用volatile修饰instance, 禁止指令重排序, 为保证多线程安全 private volatile static Singleton1 instance = null; private Singleton1() { // 防止反射调用私有构造方法(跳过安全检查), 重复实例化实例 if (instance != null) { throw new RuntimeException("error:instance=" + instance); } } public static Singleton1 getInstance() { if (instance == null) { synchronized (Singleton1.class) { if (instance == null) { instance = new Singleton1(); } } } return instance; } private Object readResolve() { return instance; // 防止反序列化重复实例化实例 } } 2. 饿汉模式, 线程安全, 效率高,

Scanning doubles when I separate decimals with comma or dot

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问题 I'm rather new to Java and I was making a simple calculator. Problem is when I my input number is for example "3.1" it gives an exception error, but when writing "3,1" it works just fine. My friend, however, has a slightly more advanced calculator (with string parsing) and when I run his code the opposite happens: 3,1 gives exception error, 3.1 works perfectly. I was looking forward to know what causes these different behaviors. I made this simple sum just now and the same happens, I'll edit