3299 Humidex

Adapted from Wikipedia, the free encyclopedia

The humidex is a measurement used by Canadian meteorologists to reflect the combined effect of heat and humidity. It differs from the heat index used in the United States in using dew point rather than relative humidity.

When the temperature is 30°C (86°F) and the dew point is 15°C (59°F), the humidex is 34 (note that humidex is a dimensionless number, but that the number indicates an approximate temperature in C). If the temperature remains 30°C and the dew point rises to 25°C (77°F), the humidex rises to 42.3.

The humidex tends to be higher than the U.S. heat index at equal temperature and relative humidity.

The current formula for determining the humidex was developed by J.M. Masterton and F.A. Richardson of Canada‘s Atmospheric Environment Service in 1979.

According to the Meteorological Service of Canada, a humidex of at least 40 causes "great discomfort" and above 45 is "dangerous." When the humidex hits 54, heat stroke is imminent.

The record humidex in Canada occurred on June 20, 1953, when Windsor, Ontario hit 52.1. (The residents of Windsor would not have known this at the time, since the humidex had yet to be invented.) More recently, the humidex reached 50 on July 14, 1995 in both Windsor and Toronto.

The humidex formula is as follows:

humidex = temperature + h
h = (0.5555)× (e - 10.0)
e = 6.11 × exp [5417.7530 × ((1/273.16) - (1/(dewpoint+273.16)))]

While humidex is just a number, radio announcers often announce it as if it were the temperature, e.g. "It‘s 47 degrees out there ... [pause] .. with the humidex,". Sometimes weather reports give the temperature and dewpoint, or the temperature and humidex, but rarely do they report all three measurements. Write a program that, given any two of the measurements, will calculate the third.

You may assume that for all inputs, the temperature, dewpoint, and humidex are all between -100°C and 100°C.

Input will consist of a number of lines. Each line except the last will consist of four items separated by spaces: a letter, a number, a second letter, and a second number. Each letter specifies the meaning of the number that follows it, and will be either T, indicating temperature, D, indicating dewpoint, or H, indicating humidex. The last line of input will consist of the single letter E.

T number D number H number

 1 #include<iostream>
 2 #include<math.h>
 3 #include<stdio.h>
 4 using namespace std;
 5 int main()
 6 {
 7     double dewpoint,temperature,humidex;
 8     char FC;
 9     while(true)
10     {
11         dewpoint=200;temperature=200;humidex=200;
12         for(int i=0;i<2;i++)
13         {
14             cin>>FC;
15             if(FC == ‘E‘)
16                 return 0;
17             else if(FC == ‘T‘)
18                 cin>>temperature;
19             else if(FC == ‘D‘)
20                 cin>>dewpoint;
21             else if(FC == ‘H‘)
22                 cin>>humidex;
23         }
24         if(humidex==200)
25         {
26             double e = 6.11 * pow(2.718281828,(5417.7530*((1/273.16)-(1/(dewpoint+273.16)))));
27             double h = 0.5555*(e-10.0);
28             humidex = temperature + h;
29         }
30         else if(temperature==200)
31         {
32             double e = 6.11 * pow(2.718281828,(5417.7530*((1/273.16)-(1/(dewpoint+273.16)))));
33             double h = 0.5555*(e-10.0);
34             temperature = humidex - h;
35         }
36         else{
37             double h = humidex - temperature;
38             double e = h/0.5555+10.0;
39             dewpoint = 1/((1/273.16)-log(e/6.11)/5417.7530)-273.16;
40         }
41 
42         printf("T %.1f D %.1f H %.1f\n",temperature,dewpoint,humidex);
43     }
44     return 0;
45 }

复习一下math.h库：

abs
原型：extern int abs(int x);
用法：#include <math.h>
功能：求整数x的绝对值
说明：计算|x|, 当x不为负时返回x，否则返回-x

fabs
原型：extern float fabs(float x);
用法：#include <math.h>
功能：求浮点数x的绝对值
说明：计算|x|, 当x不为负时返回x，否则返回-x

ceil
原型：extern float ceil(float x);
用法：#include <math.h>
功能：求不小于x的最小整数
说明：返回x的上限，如74.12的上限为75，-74.12的上限为-74。返回值为float类型。

exp
原型：extern float exp(float x);
用法：#include <math.h>
功能：求e的x次幂
说明：e=2.718281828...

floor
原型：extern float floor(float x);
用法：#include <math.h>
功能：求不大于x的最达整数
说明：返回x的下限，如74.12的下限为74，-74.12的下限为-75。返回值为float类型。

fmod
原型：extern float fmod(float x, float y);
用法：#include <math.h>
功能：计算x/y的余数
说明：返回x-n*y，符号同y。n=[x/y](向离开零的方向取整)
举例：

 1 #include<stdio.h>
 2 #include<math.h>
 3 main()
 4 {
 5     float x,y;
 6     x=74.12;
 7     y=6.4;
 8     printf("74.12/6.4: %f\n",fmod(x,y));
 9     x=74.12;
10     y=-6.4;
11     printf("74.12/(-6.4): %f\n",fmod(x,y));
12     return 0;
13 }

居然有道题目是这样的: 求 100 % 8的 优化解法。我们知道：

8刚好是2的3次方

所以 100 % 8 == 100 – math.floor(100 / 8) * 8 == 100 -  ((100 >> 3) << 3)

log
原型：extern float log(float x);
用法：#include <math.h>
功能：计算x的自然对数。
说明：x的值应大于零。

log10
原型：extern float log10(float x);
用法：#include <math.h>
功能：计算x的常用对数。
说明：x的值应大于零。

 pow10
原型：extern float pow10(float x);
用法：#include <math.h>
功能：计算10的x次幂。
说明：相当于pow(10.0,x)。

pow
原型：extern float pow(float x, float y);
用法：#include <math.h>
功能：计算x的y次幂。
说明：x应大于零，返回幂指数的结果。

sqrt
原型：extern float sqrt(float x);
用法：#include <math.h>
功能：计算x的平方根。
说明：x应大于等于零。