C#大数加减乘除取模

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

namespace 大数加减乘除
{
class Program
{
static void Main(string[] args)
{
string a = "123456";
string b = "5";
int bigger = 0;
char[] num1 = a.ToCharArray();
char[] num2 = b.ToCharArray();
bigger = num1BiggerThanNum2(num1, num2);
string num1Addnum2 = Add(num1, num2);
string num1Subnum2 = Sub(num1, num2);
string num1Mutnum2 = Mut(num1, num2);
string[] num1Desnum2 = Des(num1, num2);
}

/// <summary>
/// 加法
/// </summary>
/// <param name="num1"></param>
/// <param name="num2"></param>
/// <returns>返回结果</returns>
public static string Add(char[] num1, char[] num2)
{
//对两个加数进行初始化，使长度相同
if (num1.Length > num2.Length)
num2 = InitString(num1, num2);
if (num1.Length < num2.Length)
num1 = InitString(num1, num2);
string result = "";
string finalRes = "";
//每一位相加都保留进位
int jinwei = 0;
for (int i = num1.Length - 1; i >= 0; i--)
{
//将字符转换为数字
int res = num1[i] + num2[i] - 2 * '0' + jinwei;
jinwei = 0;
if (res >= 10)
{
jinwei = 1;
res -= 10;
}
result += res;
}
if (jinwei > 0)
result += jinwei;
//将结果反转
for (int i = result.Length - 1; i >= 0; i--)
{
finalRes += result[i];
}
//移除不必要的零
finalRes = RemoveZero(finalRes);
return finalRes;
}

/// <summary>
/// 减法
/// </summary>
/// <param name="num1"></param>
/// <param name="num2"></param>
/// <returns>返回结果</returns>
public static string Sub(char[] num1, char[] num2)
{
string result = "";
string finalRes = "";
//保留两个数相减的借位，用于下一位计算
int jiewei = 0;
//判断两个数的大小，决定是否加“-”号
int bigger = num1BiggerThanNum2(num1, num2);
if (bigger < 0)
{
char[] c = num1;
num1 = num2;
num2 = c;
finalRes += '-';
}
if (bigger == 0)
return "0";
//将两个数初始化，使位数相同
if (num1.Length > num2.Length)
num2 = InitString(num1, num2);
if (num1.Length < num2.Length)
num1 = InitString(num1, num2);
for (int i = num1.Length - 1; i >= 0; i--)
{
//两数相减，不需要将字符转换为数字
int res = num1[i] - num2[i] - jiewei;
jiewei = 0;
if (res < 0)
{
res += 10;
jiewei = 1;
}
result += res;
}
//将结果反转
for (int i = result.Length - 1; i >= 0; i--)
{
finalRes += result[i];
}
finalRes = RemoveZero(finalRes);
return finalRes;
}

/// <summary>
/// 乘法
/// </summary>
/// <param name="num1"></param>
/// <param name="num2"></param>
/// <returns>返回结果</returns>
public static string Mut(char[] num1, char[] num2)
{
string finalRes = "0";
//判断大小，将较大的数放到上方，较小的数用来乘较大的数
int bigger = num1BiggerThanNum2(num1, num2);
if (bigger < 0)
{
char[] c = num1;
num1 = num2;
num2 = c;
}
//两个数相乘的进位，用于计算
int jinwei = 0;
for (int i = 0; i < num2.Length; i++)
{
string result = "";
string str = "";
for (int j = num1.Length - 1; j >= 0; j--)
{
int res = (num1[j] - '0') * (num2[num2.Length - i - 1] - '0') + jinwei;
jinwei = 0;
if (res >= 10)
{
int temp = res;
res = res % 10;
jinwei = temp / 10;
}
str += res;
}
if (jinwei > 0)
str += jinwei;
//将每一位相乘的结果反转
for (int k = str.Length - 1; k >= 0; k--)
{
result += str[k];
}
//每相乘一位，都需要在末尾加零
for (int k = 0; k < i; k++)
{
result += "0";
}
//将每一位相乘的结果与之前的结果相加
finalRes = Add(finalRes.ToCharArray(), result.ToCharArray());
}

return finalRes;
}

/// <summary>
/// 除法
/// </summary>
/// <param name="num1"></param>
/// <param name="num2"></param>
/// <returns>返回的字符数组中，第一个元素代表商，第二个元素代表余数</returns>
public static string[] Des(char[] num1, char[] num2)
{
string[] finalRes = new string[2];
//判断两个数的大小，如果除数大于被除数，则直接返回结果
int bigger = num1BiggerThanNum2(num1, num2);
if (bigger < 0)
{
finalRes[0] = "0";
for (int i = 0; i < num1.Length; i++)
{
finalRes[1] += num1[i];
}
}
else if (bigger == 0)
{
finalRes[0] = "1";
finalRes[1] = "0";
}
else//除数小于被除数
{
//被除数，从除数的位数开始逐个记录
string beichushu = "";
string shang = "";
for (int i = 0; i < num2.Length; i++)
{
beichushu += num1[i];
}
int flag = num2.Length - 1;
for (int i = num2.Length - 1; i < num1.Length - 1; i++)
{
//第一轮除法计算完成，添加被除数下一位
if (num1BiggerThanNum2(beichushu.ToCharArray(), num2) < 0)
{

if (i + 1 == num1.Length)
break;
beichushu += num1[i + 1];
}
//判断当前被除数是否大于除数，如果小于则添加被除数下一位
if (num1BiggerThanNum2(beichushu.ToCharArray(), num2) < 0)
{

if (i + 1 == num1.Length)
break;
beichushu += num1[i + 1];
shang += "0";
continue;
}
//判断当前除数与被除数大小，如果两数相等，则被除数减为0，商为1
if (num1BiggerThanNum2(beichushu.ToCharArray(), num2) == 0)
{
beichushu = "0";
shang += "1";
}
//当除数小于被除数，则进行减法计算，看能够被多少个除数除
if (num1BiggerThanNum2(beichushu.ToCharArray(), num2) > 0)
{
string currentShang = "0";
for (int j = 1; num1BiggerThanNum2(beichushu.ToCharArray(), num2) >= 0; j++)
{
beichushu = Sub(beichushu.ToCharArray(), num2);
currentShang = j.ToString();
}
shang += currentShang;
}
}
//将结果中多余的零去除
finalRes[0] = RemoveZero(shang);

finalRes[1] = RemoveZero(beichushu);
//如果商为0，则返回0
if (finalRes[1] == "")
finalRes[1] = "0";
}
return finalRes;
}

/// <summary>
/// 将两个字符串进行初始化，以达到相同的长度，在较短的字符串前边补零
/// </summary>
/// <param name="a"></param>
/// <param name="b"></param>
/// <returns>返回初始化后的字符串</returns>
public static char[] InitString(char[] a, char[] b)
{
int aLength = a.Length;
int bLength = b.Length;
char[] c = new char[Math.Max(aLength, bLength)];
int start = Math.Abs(aLength - bLength);
for (int i = 0; i < Math.Max(aLength, bLength); i++)
{
if (i < start)
c[i] = '0';
else
{
if (aLength > bLength)
c[i] = b[i - start];
if (aLength < bLength)
c[i] = a[i - start];
}
}
return c;
}

/// <summary>
/// 判断两个数的大小
/// </summary>
/// <param name="num1"></param>
/// <param name="num2"></param>
/// <returns>num1大于num2，则返回1；num1等于num2，则返回0；num1小于num2，则返回-1；</returns>
public static int num1BiggerThanNum2(char[] num1, char[] num2)
{
if (num1.Length > num2.Length)
{
return 1;
}
if (num1.Length < num2.Length)
{
return -1;
}
if (num1.Length == num2.Length)
{
for (int i = 0; i < num2.Length; i++)
{
if (num1[i] > num2[i])
return 1;
else if (num1[i] < num2[i])
return -1;
}
}
return 0;
}

/// <summary>
/// 移除字符串前边不必要的零
/// </summary>
/// <param name="str"></param>
/// <returns>返回正确字符串</returns>
public static string RemoveZero(string str)
{
string result = "";
bool start = false;
for (int i = 0; i < str.Length; i++)
{
if (str[i] != '0')
{
start = true;
}
if (start)
result += str[i];
}
return result;
}
}
}