【C++标准库】数值组件

随机数

使用随机数程序库，需包含头文件<random>。常用的属于随机数生成器指的是一个引擎和一个分布的组合。

引擎作为随机数的源头，它们是function object,能够产生随机的无符号值，并均匀分布于一个预定义的最大值和最小值之间。每次以operator()调用它，其内部状态会发生改变，使得此后可产生出一个新的随机值。

分布表示以何种方法将这些随机值转换为随机数。后者分布于由使用者指定的参数所指定的区间内。

int main(int argc, char** argv)
{
    default_random_engine dre; //使用默认引擎
    uniform_int_distribution<int> di(10, 20);  //闭区间[10,20]
    for (int i = 0;i < 20;++i)
    {
        cout << di(dre) << " ";
    }
    cout << endl;
    uniform_real_distribution<double> dr(10.0, 20.0); //半开区间[10.0,20.0)
    for (int i = 0;i < 8;++i)
    {
        cout << dr(dre) << " ";
    }
    cout << endl;
    vector<int> v = { 1,2,3,4,5,6,7,8,9 };
    shuffle(v.begin(), v.end(), dre);
    for (auto e : v)
    {
        cout << e << " ";
    }
    cout << endl;
}

任何引擎的初始状态都有明确定义，并非随机的。如果需要产生一个不可预期的随机数，需要传递一个种子seed给引擎构造函数。

复数

定义于头文件<complex>中

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference, 2nd Edition"
* by Nicolai M. Josuttis, Addison-Wesley, 2012
*
* (C) Copyright Nicolai M. Josuttis 2012.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <complex>
using namespace std;

int main()
{
    // complex number with real and imaginary parts
    // - real part: 4.0
    // - imaginary part: 3.0
    complex<double> c1(4.0, 3.0);

    // create complex number from polar coordinates
    // - magnitude: 5.0
    // - phase angle: 0.75
    complex<float> c2(polar(5.0, 0.75));

    // print complex numbers with real and imaginary parts
    cout << "c1: " << c1 << endl;
    cout << "c2: " << c2 << endl;

    // print complex numbers as polar coordinates
    cout << "c1: magnitude: " << abs(c1)
        << " (squared magnitude: " << norm(c1) << ") "
        << " phase angle: " << arg(c1) << endl;
    cout << "c2: magnitude: " << abs(c2)
        << " (squared magnitude: " << norm(c2) << ") "
        << " phase angle: " << arg(c2) << endl;

    // print complex conjugates
    cout << "c1 conjugated:  " << conj(c1) << endl;
    cout << "c2 conjugated:  " << conj(c2) << endl;

    // print result of a computation
    cout << "4.4 + c1 * 1.8: " << 4.4 + c1 * 1.8 << endl;

    // print sum of c1 and c2:
    // - note: different types
    cout << "c1 + c2:        "
        << c1 + complex<double>(c2.real(), c2.imag()) << endl;

    // add square root of c1 to c1 and print the result
    cout << "c1 += sqrt(c1): " << (c1 += sqrt(c1)) << endl;
}

全局数值函数

头文件<cmath>和<cstdlib>提供自C继承而来的全局数值函数。