写一个C语言处理BigInteger数的函数

好的，下面是一个处理BigInteger数的C语言函数：

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

#define SIZE 1000

// 将字符串转为大整数
void str_to_bigint(char* str, int len, int* bigint) {
    for (int i = 0; i < len; i++) {
        bigint[len - i - 1] = str[i] - '0';
    }
}

// 将大整数转为字符串
void bigint_to_str(int* bigint, int len, char* str) {
    for (int i = 0; i < len; i++) {
        str[i] = bigint[len - i - 1] + '0';
    }
    str[len] = '\0';
}

// 大整数相加
void bigint_add(int* a, int* b, int* c, int len_a, int len_b, int* len_c) {
    memset(c, 0, sizeof(int) * SIZE);
    int carry = 0, i;
    for (i = 0; i < len_a && i < len_b; i++) {
        int tmp = a[i] + b[i] + carry;
        c[i] = tmp % 10;
        carry = tmp / 10;
    }
    while (i < len_a) {
        int tmp = a[i] + carry;
        c[i] = tmp % 10;
        carry = tmp / 10;
        i++;
    }
    while (i < len_b) {
        int tmp = b[i] + carry;
        c[i] = tmp % 10;
        carry = tmp / 10;
        i++;
    }
    if (carry) {
        c[i] = carry;
        i++;
    }
    *len_c = i;
}

// 大整数相减
void bigint_sub(int* a, int* b, int* c, int len_a, int len_b, int* len_c) {
    memset(c, 0, sizeof(int) * SIZE);
    int borrow = 0, i;
    for (i = 0; i < len_a && i < len_b; i++) {
        int tmp = a[i] - b[i] - borrow;
        if (tmp < 0) {
            tmp += 10;
            borrow = 1;
        } else {
            borrow = 0;
        }
        c[i] = tmp;
    }
    while (i < len_a) {
        int tmp = a[i] - borrow;
        if (tmp < 0) {
            tmp += 10;
            borrow = 1;
        } else {
            borrow = 0;
        }
        c[i] = tmp;
        i++;
    }
    *len_c = i;
    while (*len_c > 1 && c[*len_c - 1] == 0) {
        (*len_c)--;
    }
}

// 大整数相乘
void bigint_mul(int* a, int* b, int* c, int len_a, int len_b, int* len_c) {
    memset(c, 0, sizeof(int) * SIZE);
    for (int i = 0; i < len_b; i++) {
        int carry = 0;
        for (int j = 0; j < len_a; j++) {
            int tmp = a[j] * b[i] + c[i+j] + carry;
            c[i+j] = tmp % 10;
            carry = tmp / 10;
        }
        c[i+len_a] += carry;
    }
    *len_c = len_a + len_b;
    while (*len_c > 1 && c[*len_c - 1] == 0) {
        (*len_c)--;
    }
}

// 大整数相除
void bigint_div(int* a, int* b, int* c, int len_a, int len_b, int* len_c) {
    memset(c, 0, sizeof(int) * SIZE);
    int tmp[SIZE], tmp_len = 0;
    for (int i = 0; i < len_a; i++) {
        tmp[tmp_len++] = a[len_a-i-1];
        if (tmp_len == 1 && tmp[0] == 0) {
            tmp_len--;
        }
        int j = tmp_len - 1;
        while (j >= 0 && bigint_cmp(tmp, tmp_len, b, len_b) < 0) {
            tmp[++j] = 0;
            tmp_len++;
        }
        while (j >= 0) {
            int r = bigint_divide(tmp, tmp_len, b, len_b);
            c[i] += r;
            for (int k = tmp_len - 1; k >= 0; k--) {
                if (k > 0) {
                    tmp[k] = tmp[k-1];
                } else {
                    tmp[k] = 0;
                }
            }
            tmp_len--;
            if (tmp_len > 0 && tmp[tmp_len - 1] == 0) {
                tmp_len--;
            }
            j--;
        }
    }
    *len_c = len_a;
    while (*len_c > 1 && c[*len_c - 1] == 0) {
        (*len_c)--;
    }
}

// 比较两个大整数的大小，返回值小于0表示a<b，等于0表示a=b，大于0表示a>b
int bigint_cmp(int* a, int len_a, int* b, int len_b) {
    while (len_a > 1 && a[len_a - 1] == 0) {
        len_a--;
    }
    while (len_b > 1 && b[len_b - 1] == 0) {
        len_b--;
    }
    if (len_a < len_b) {
        return -1;
    } else if (len_a > len_b) {
        return 1;
    } else {
        for (int i = len_a - 1; i >= 0; i--) {
            if (a[i] < b[i]) {
                return -1;
            } else if (a[i] > b[i]) {
                return 1;
            }
        }
        return 0;
    }
}

// 用大整数b除以大整数a，返回余数
int bigint_divide(int* a, int len_a, int* b, int len_b) {
    int l = 0, r = 10;
    while (l < r) {
        int mid = (l + r + 1) / 2;
        int ta[SIZE], ta_len;
        memset(ta, 0, sizeof(int) * SIZE);
        ta[0] = mid;
        bigint_mul(ta, a, ta, 1, len_a, &ta_len);
        if (bigint_cmp(ta, ta_len, b, len_b) <= 0) {
            l = mid;
        } else {
            r = mid - 1;
        }
    }
    return l;
}

int main() {
    char str_a[SIZE], str_b[SIZE];
    int bigint_a[SIZE], bigint_b[SIZE], bigint_c[SIZE], len_a, len_b, len_c;

    // 输入两个字符串表示的大整数
    printf("Please input integer a:");
    scanf("%s", str_a);
    len_a = strlen(str_a);
    str_to_bigint(str_a, len_a, bigint_a);

    printf("Please input integer b:");
    scanf("%s", str_b);
    len_b = strlen(str_b);
    str_to_bigint(str_b, len_b, bigint_b);

    // 大整数加法
    bigint_add(bigint_a, bigint_b, bigint_c, len_a, len_b, &len_c);
    char str_c[SIZE];
    bigint_to_str(bigint_c, len_c, str_c);
    printf("a + b = %s\n", str_c);

    // 大整数减法
    bigint_sub(bigint_a, bigint_b, bigint_c, len_a, len_b, &len_c);
    bigint_to_str(bigint_c, len_c, str_c);
    printf("a - b = %s\n", str_c);

    // 大整数乘法
    bigint_mul(bigint_a, bigint_b, bigint_c, len_a, len_b, &len_c);
    bigint_to_str(bigint_c, len_c, str_c);
    printf("a * b = %s\n", str_c);

    // 大整数除法
    bigint_div(bigint_b, bigint_a, bigint_c, len_b, len_a, &len_c);
    bigint_to_str(bigint_c, len_c, str_c);
    printf("b / a = %s\n", str_c);

    return 0;
}

这个函数可以处理大于long long所能表示的整数，通过字符串转为大整数的方式进行计算，支持加、减、乘、除等操作。