大整数乘法分治法的c++代码

以下是大整数乘法分治法的C代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// 用于将字符转换为数字
int char_to_int(char c)
{
    return (int)(c - '0');
}

// 用于将数字转换为字符
char int_to_char(int n)
{
    return (char)(n + '0');
}

// 用于将字符串表示的数字转换为整数数组
void string_to_array(char *str, int *a, int len)
{
    int i, j;

    for (i = 0, j = len - 1; i < len; i++, j--) {
        a[i] = char_to_int(str[j]);
    }
}

// 用于将整数数组表示的数字转换为字符串
void array_to_string(int *a, int len, char *str)
{
    int i, j;

    for (i = len - 1, j = 0; i >= 0; i--, j++) {
        str[j] = int_to_char(a[i]);
    }
    str[len] = '\0';
}

// 用于向数组中添加零
void append_zero(int *a, int len, int n)
{
    int i;

    for (i = len; i < len + n; i++) {
        a[i] = 0;
    }
}

// 用于删除数组中前导零
int remove_leading_zeros(int *a, int len)
{
    int i;

    for (i = len - 1; i > 0; i--) {
        if (a[i] != 0) {
            break;
        }
    }
    return i + 1;
}

// 用于将两个整数数组相加
void add(int *a, int *b, int *c, int len)
{
    int i, carry = 0;

    for (i = 0; i < len; i++) {
        c[i] = a[i] + b[i] + carry;
        carry = c[i] / 10;
        c[i] %= 10;
    }

    if (carry > 0) {
        c[i] = carry;
    }
}

// 用于将两个整数数组相减
void subtract(int *a, int *b, int *c, int len)
{
    int i, borrow = 0;

    for (i = 0; i < len; i++) {
        c[i] = a[i] - b[i] - borrow;

        if (c[i] < 0) {
            c[i] += 10;
            borrow = 1;
        } else {
            borrow = 0;
        }
    }
}

// 用于将两个整数数组相乘
void multiply(int *a, int *b, int *c, int len)
{
    if (len == 1) {
        c[0] = a[0] * b[0];
        return;
    }

    int i, j, k;

    int *a1 = (int *)malloc(len / 2 * sizeof(int));
    int *b1 = (int *)malloc(len / 2 * sizeof(int));
    int *c1 = (int *)malloc(len * sizeof(int));

    int *a2 = (int *)malloc(len / 2 * sizeof(int));
    int *b2 = (int *)malloc(len / 2 * sizeof(int));
    int *c2 = (int *)malloc(len * sizeof(int));

    int *a1b1 = (int *)malloc(len * sizeof(int));
    int *a2b2 = (int *)malloc(len * sizeof(int));
    int *tmp = (int *)malloc(len * sizeof(int));

    memset(a1, 0, len / 2 * sizeof(int));
    memset(b1, 0, len / 2 * sizeof(int));
    memset(c1, 0, len * sizeof(int));

    memset(a2, 0, len / 2 * sizeof(int));
    memset(b2, 0, len / 2 * sizeof(int));
    memset(c2, 0, len * sizeof(int));

    memset(a1b1, 0, len * sizeof(int));
    memset(a2b2, 0, len * sizeof(int));
    memset(tmp, 0, len * sizeof(int));

    for (i = 0; i < len / 2; i++) {
        a1[i] = a[i];
        b1[i] = b[i];
    }

    for (i = len / 2; i < len; i++) {
        a2[i - len / 2] = a[i];
        b2[i - len / 2] = b[i];
    }

    multiply(a1, b1, c1, len / 2);
    multiply(a2, b2, c2, len / 2);
    add(a1, a2, tmp, len / 2);
    add(b1, b2, tmp + len / 2, len / 2);
    multiply(tmp, tmp + len / 2, a1b1, len / 2 + 1);
    subtract(a1b1, c1, a1b1, len * 2);
    subtract(a1b1, c2, a1b1, len * 2 - (len / 2));
    append_zero(a1b1, len * 2 - (len / 2), len / 2);
    add(c1, a1b1, c1, len * 2);
    append_zero(c2, len, len / 2);
    add(c1, c2, c, len * 2);
    free(a1);
    free(b1);
    free(c1);
    free(a2);
    free(b2);
    free(c2);
    free(a1b1);
    free(a2b2);
    free(tmp);
}

int main()
{
    char a[1001];
    char b[1001];
    int len1, len2, len, i;
    int *num1, *num2, *result;

    scanf("%s", a);
    scanf("%s", b);

    len1 = strlen(a);
    len2 = strlen(b);
    len = len1 > len2 ? len1 : len2;

    num1 = (int *)malloc(len * sizeof(int));
    num2 = (int *)malloc(len * sizeof(int));
    result = (int *)malloc(len * 2 * sizeof(int));
    memset(num1, 0, len * sizeof(int));
    memset(num2, 0, len * sizeof(int));
    memset(result, 0, len * 2 * sizeof(int));

    string_to_array(a, num1, len1);
    string_to_array(b, num2, len2);

    multiply(num1, num2, result, len);

    i = remove_leading_zeros(result, len * 2);

    if (i == 0) {
        printf("0\n");
    } else {
        array_to_string(result, i, a);
        printf("%s\n", a);
    }

    free(num1);
    free(num2);
    free(result);

    return 0;
}