C#, Lesson 19 of "Xiaobai Programming": Random Number (Random) Sixth, Randomly Generate Large Numbers of Any Length (BigInteger)

1 text format

using System;
using System.Linq;
using System.Text;
using System.Collections.Generic;

/// <summary>
/// The four arithmetic operations of large numbers (addition, subtraction, multiplication and division) and factorial operation
/// The multiplication calculation includes the primary school student algorithm, Karatsuba and Toom-Cook3 algorithm
/// The division operation is Truffer's own algorithm;
// / </summary>
public static class BigInteger_Utility
{     /// <summary>     /// Record the number of addition, subtraction, multiplication and division operations     /// </summary>     public static int[] operations { get; set; } = new int[] { 0, 0, 0, 0 };

    /// <summary>
    /// Lesson 19 of "Xiaobai Programming": Random Number (Random) Sixth, randomly generate large numbers of any length (BigInteger)
    /// Generally, numbers exceeding 9 digits can be Become a "big number".
    /// The four arithmetic operations between two large numbers are used in cryptography, high-precision calculations and other applications.
    /// Floating point numbers with many digits can be converted into large numbers and then reversed.
    /// </summary>
    /// <param name="n"></param>
    /// <returns></returns>
    public static string rand(int n)
    {         // Random number generator         Random rnd = new Random();         StringBuilder sb = new StringBuilder();         // The first number cannot be 0, so: a random number between 0-8 + 1 = 1-9         sb.Append((rnd.Next(9) + 1).ToString());         // The next n-1 numbers are 0-9; counting starts from 1         for (int i = 1; i < n; i++)         {








            sb.Append((rnd.Next(10)).ToString());
        }
        return sb.ToString();
    }

    /// <summary>
    /// Convert string numbers to arrays
    /// Low digit (right) first, such as "123", n=6 is stored as 3,2,1,_,_,_
    // / n may be greater than the length of a; the remaining positions are reserved for carry, etc.
    /// </summary>
    /// <param name="a"></param>
    /// <param name="n">Maximum number of digits, followed by 0</param>
    /// <returns> </returns>
    public static int[] string_to_digitals(string a, int n)
    {         // Convert string to "character array"         char[] c = a.ToCharArray();         // Array to store numbers         int[] d = new int[n];         // Starting from the rightmost (ones digit) number, transfer it to a digital array and participate in the subsequent calculation         for (int i = a.Length - 1,









            // The '0' character is the smallest numeric character
            // value = character - '0' ;
            d[j++] = a[i] - '0';
        }
        return d;
    }

    /// <summary>
    /// Convert array number to string type
    /// Low digit (right) first, such as 3,2,1,_,_,_ converted to "123", n=6
    // / This is the reverse calculation function of the previous string_to_digitals
    /// n may be greater than the length of d; the remaining positions are reserved for carry, etc.
    /// </summary>
    /// <param name="d"></param>
    /// <returns></returns>
    public static string digitals_to_string(int[] d)
    {         int n = d.









            StringBuilder sb = new StringBuilder();
            for (; k >= 0; k--) sb.Append(d[k]);
            return sb.ToString();
        }
        else
        {
            return "0";
        }
    }
}

2 code format

using System;
using System.Linq;
using System.Text;
using System.Collections.Generic;

/// <summary>
/// 大数的（加减乘除）四则运算、阶乘运算
/// 乘法计算包括小学生算法、Karatsuba和Toom-Cook3算法
/// 除法运算为 Truffer 自创算法；
/// </summary>
public static class BigInteger_Utility
{
    /// <summary>
    /// 记录 加减乘除 的运算次数
    /// </summary>
    public static int[] operations { get; set; } = new int[] { 0, 0, 0, 0 };

    /// <summary>
    /// 《小白学程序》第十九课：随机数（Random）第六，随机生成任意长度的大数（BigInteger）
    /// 一般可将超过9位数的数字成为“大数”。
    /// 两个大数之间的四则运算用于密码学、高精度计算等应用。
    /// 位数很多的浮点数可转为大数，再逆转即可。
    /// </summary>
    /// <param name="n"></param>
    /// <returns></returns>
    public static string rand(int n)
    {
        // 随机数发生器
        Random rnd = new Random();
        StringBuilder sb = new StringBuilder();
        // 第一个数字不能为0，故：0-8之间的随机数+ 1 = 1-9
        sb.Append((rnd.Next(9) + 1).ToString());
        // 后面 n-1 个数字为 0-9；从 1 开始计数
        for (int i = 1; i < n; i++)
        {
            sb.Append((rnd.Next(10)).ToString());
        }
        return sb.ToString();
    }

    /// <summary>
    /// 字符串型的数字转为数组
    /// 低位（右）在前，比如 "123" , n=6 存为 3,2,1,_,_,_
    /// n 可能大于 a 的长度；剩余位置留出来用于 进位 等。
    /// </summary>
    /// <param name="a"></param>
    /// <param name="n">最大位数，后面留0</param>
    /// <returns></returns>
    public static int[] string_to_digitals(string a, int n)
    {
        // 字符串 转为 “字符数组”
        char[] c = a.ToCharArray();
        // 存储数字的数组
        int[] d = new int[n];
        // 从最右端（个位）数字开始，转存为数字数组，参与后面的计算
        for (int i = a.Length - 1, j = 0; i >= 0; i--)
        {
            // 跳过数字前面可能有的 - 号
            if (a[i] == '-') continue;
            // '0' 字符是最小的数字字符
            // 数值 = 字符 - '0' ；
            d[j++] = a[i] - '0';
        }
        return d;
    }

    /// <summary>
    /// 数组型数字转为字符串型
    /// 低位（右）在前，比如 3,2,1,_,_,_ 转为 "123", n=6
    /// 这是前面 string_to_digitals 的反向计算函数
    /// n 可能大于 d 的长度；剩余位置留出来用于 进位 等。
    /// </summary>
    /// <param name="d"></param>
    /// <returns></returns>
    public static string digitals_to_string(int[] d)
    {
        int n = d.Length;
        // 数字数组 d 含有一些无效的数组；
        // 因此，先从最右段开始去除无效的位置
        int k = n - 1;
        //for (; (k >= 0) && (d[k] == 0); k--) ;
        while ((k >= 0) && (d[k] == 0)) k--;
        // 找到有效位置后，开始组合字符串；
        if (k >= 0)
        {
            StringBuilder sb = new StringBuilder();
            for (; k >= 0; k--) sb.Append(d[k]);
            return sb.ToString();
        }
        else
        {
            return "0";
        }
    }
}