高精度减法--C++

仿照竖式减法，先对其，再对应位相减。

算法处理时，先比较大小，用大的减小的，对应位再比较大小，用于作为借位符。

#include <iostream>

#include <cstring>

#define MAXSIZE 20

#define MAXOUTSIZE MAXSIZE + 2

using namespace std;

int main()

{

    char a[MAXSIZE] = {'0'},

         b[MAXSIZE] = {'0'},

         c[MAXOUTSIZE] = {'\0'},

         t[MAXSIZE] = {'0'};

    int a_int[MAXSIZE] = {0},

        b_int[MAXSIZE] = {0},

        c_int[MAXOUTSIZE] = {0};

    cin >> a;

    cin >> b;

    memset(a_int, 0, sizeof a_int);

    memset(b_int, 0, sizeof b_int);

    memset(c_int, 0, sizeof c_int);

	//考虑是否交换，大数减小数

    bool minus = false;

    if ((strlen(a) < strlen(b)) ||

        (strcmp(a, b) < 0))

    {

        strcpy(t, a);

        strcpy(a, b);

        strcpy(b, t);

        minus = true;

    }

    if(minus)

    {

        cout << "-";

    }

    int len_a = strlen(a), len_b = strlen(b);

    //对齐

    for (int i = len_a - 1, j = 0; i >= 0; i--, j++)

    {

        a_int[j] = a[i] - '0';

    }

    for (int i = len_b - 1, j = 0; i >= 0; i--, j++)

    {

        b_int[j] = b[i] - '0';

    }

    //对应位相减

    for (int i = 0; i < MAXSIZE; i++)

    {

        //考虑是否借位

        if (a_int[i] < b_int[i])

        {

            a_int[i] += 10;

            a_int[i + 1]--;

        }

        c_int[i] = a_int[i] - b_int[i];

    }

    int ans_len = 0;

    for (int i = 0; i < MAXOUTSIZE - 1; i++)

    {

        c_int[i + 1] += c_int[i] / 10;

        c_int[i] %= 10;

        ans_len = i;

    }

    while (c_int[ans_len] == 0)

    {

        ans_len--;

    }

    if (ans_len < 0)

    {

        cout << "0";

        return 0;

    }

    for (int i = ans_len; i >= 0; i--)

    {

        c[i] = c_int[i] + '0';

    }

    for (int i = MAXOUTSIZE - 1; i >= 0; i--)

    {

        if ('\0' != c[i])

        {

            cout << c[i];

        }

    }

    return 0;

}