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App Inventor 2开发简单计算器 - App Inventor 2 中文网 - 清泛IT论坛，有思想、有深度
...会出现一些莫名其妙的状况，这里要讲解的是一个只有20个按键的简易计算器，实现了加减乘除的简单运算，以及清除、回退、求相反数等，如图2-1所示，更为复杂的运算，如求乘方、方根及三角函数的运算，可以利用开发工具...
What's the point of malloc(0)?
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According to the specifications, malloc(0) will return either "a null pointer or a unique pointer that can be successfully passed to free()".
This basically lets you allocate nothing, but still pass the "artist" variable to a call to free() without worry. For pra...
remove None value from a list without removing the 0 value
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10 Answers
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计算统计特征（正态分布）函数及实例 - C/C++ - 清泛网 - 专注C/C++及内核技术
...ain(int argc, _TCHAR* argv[])
{
std::map<int, int> map_test;
map_test[0] = 100;
map_test[5] = 80;
map_test[2] = 10;
map_test[8] = 99;
map_test[4] = 102;
StdevInfo stdev_info;
stdev_info.init();
stdev_info.caculate_stdev_info(map_test.begin(), map_test.end(),
[](const std::p...
Moving matplotlib legend outside of the axis makes it cutoff by the figure box
...plt
import numpy as np
plt.gcf().clear()
x = np.arange(-2*np.pi, 2*np.pi, 0.1)
fig = plt.figure(1)
ax = fig.add_subplot(111)
ax.plot(x, np.sin(x), label='Sine')
ax.plot(x, np.cos(x), label='Cosine')
ax.plot(x, np.arctan(x), label='Inverse tan')
handles, labels = ax.get_legend_handles_labels()
lgd =...
MySQL ERROR 1045 (28000): Access denied for user 'bill'@'localhost' (using password: YES)
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You probably have an anonymous user ''@'localhost' or ''@'127.0.0.1'.
As per the manual:
When multiple matches are possible, the server must determine which of
them to use. It resolves this issue as follows: (...)
When a client attempts to connect, the server looks throug...
How to draw a rounded Rectangle on HTML Canvas?
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50
The HTML5 canvas doesn't provide a method to draw a rectangle with rounded corners.
How about u...
What does {0} mean when initializing an object?
When {0} is used to initialize an object, what does it mean? I can't find any references to {0} anywhere, and because of the curly braces Google searches are not helpful.
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In php, is 0 treated as empty?
...ollowing things are considered to be empty:
"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
var $var; (a variable declared, but without a value in a class)
Note that this is exactly the same list as for a ...
httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for Se
I tried to restart my Apache server on CentOS 5.0 and got this message:
11 Answers
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