C语言BigInteger

最新推荐文章于 2021-05-24 10:27:53 发布

原创最新推荐文章于 2021-05-24 10:27:53 发布 · 1.8k 阅读

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这篇博客介绍了作者使用C语言编写的初步版BigInteger库，包括大数的加法、乘法和除法运算。虽然存在一些未处理的细节，但对于初学者来说已足够入门。

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C写的大数加乘除法，中间有些细节没有处理，不过基本凑和用，算个初版本吧，刚用C不久不熟练啊

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

void reverse(char *s)
{
    int len = strlen(s);
    int i, j;
    char c;
    for (i = 0, j = len - 1; i < j; i++, j--)
    {
        c = *(s + i);
        *(s + i) = *(s + j);
        *(s + j) = c;
    }
}

char *removeHeadZero(char *s)
{
    char *r;
    while (*s++ == '0')
        ;
    r = --s;
    return r;
}

char *appendTailZero(char *s, int zeros)
{
    int i, len = strlen(s);
    char *r = malloc(len + zeros + 1);
    for (i = 0; i < len; i++)
        *(r + i) = *(s + i);
    for (i = len; i < len + zeros; i++)
        *(r + i) = '0';
    *(r + len + zeros) = '\0';
    return r;
}

char *add(char *s1, char *s2)
{
    int l1 = strlen(s1);
    int l2 = strlen(s2);
    int len = l1 > l2 ? l1 : l2;
    char *r = malloc(len + 2);
    int i, prev = 0, a, b, sum;
    for (i = 0; i < len; i++)
    {
        a = l1 - 1 - i >= 0 ? *(s1 + l1 - 1 - i) - '0' : 0;
        b = l2 - 1 - i >= 0 ? *(s2 + l2 - 1 - i) - '0' : 0;
        sum = a + b + prev;
        *(r + i) = sum > 9 ? sum - 10 + '0' : sum + '0';
        prev = sum > 9 ? 1 : 0;
    }
    if (prev)
    {
        *(r + len) = '1';
        *(r + len + 1) = '\0';
    }
    else
        *(r + len) = '\0';
    reverse(r);
    return r;
}

char *multiplyHelper(char *s1, int digit)
{
    int i, res, prev = 0, len = strlen(s1);
    char *r = malloc(len + 2);
    if (!digit)
    {
        *r = '0';
        *(r + 1) = '\0';
        return r;
    }

    for (i = 0; i < len; i++)
    {
        res = (*(s1 + len - 1 - i) - '0') * digit + prev;
        *(r + i) = res % 10 + '0';
        prev = res / 10;
    }
    if (prev)
    {
        *(r + len) = prev + '0';
        *(r + len + 1) = '\0';
    }
    else
        *(r + len) = '\0';
    reverse(r);
    return r;
}

char *multiply(char *s1, char *s2)
{
    if (strlen(s1) < strlen(s2))
    {
        char *temp;
        temp = s1;
        s1 = s2;
        s2 = temp;
    }
    int l2 = strlen(s2);
    int i;
    char *t, *zt;
    char *sum = malloc(2);
    sum = "0";
    for (i = 0; i < l2; i++)
    {
        char *tp = sum;
        t = multiplyHelper(s1, *(s2 + l2 - 1 - i) - '0');
        zt = appendTailZero(t, i);
        sum = add(tp, zt);
        free(t);
        free(tp);
        free(zt);
    }
    return sum;
}

char *divide(char *s, int num, int *remain)
{
    int i, rem = 0, len = strlen(s);
    char *r = malloc(len + 1);
    for (i = 0; i < len; i++)
    {
        rem = rem * 10 + *(s + i) - '0';
        *(r + i) = rem / num + '0';
        rem %= num;
    }
    *remain = rem;
    *(r + len) = '\0';
    r = removeHeadZero(r);
    if (!strlen(r))
    {
        *r = '0';
        *(r + 1) = '\0';
    }
    return r;
}

int main()
{
    char s1[] = "123";
    char s2[] = "456";
    printf(add(s1, s2));
    printf("\n");

    printf(add("99999", "98765"));
    printf("\n");
    printf(add("99999", "123"));
    printf("\n");
    printf(multiplyHelper("96899", 9));
    printf("\n");
    printf(multiplyHelper("96899", 0));
    printf("\n");
    printf(appendTailZero("96899", 3));
    printf("\n");
    printf(multiply("1234", "456"));
    printf("\n");
    printf(multiply("789", "4560"));
    printf("\n");
    printf(multiply("789", "0"));
    printf("\n");
    printf(multiply("0", "4560"));
    printf("\n");
    printf(multiply("0", "0"));
    printf("\n");
    int p;
    printf(divide("123456", 456, &p));
    printf("\n");
    printf("%d\n", p);
    return 0;
}