程序代码：

char *add(char *a, char *b)
{
    char temp[STR_LEN];
    size_t len_a, len_b, len_result;
    int carry1 = 0, carry2 = 0;
    unsigned i, j;

    if (strlen(a) < strlen(b))
    {
        strcpy(temp, a);
        strcpy(a, b);
        strcpy(b, temp);
    }

    len_a = strlen(a);
    len_b = strlen(b);
    char *result = (char *)malloc(sizeof(char) * (len_a + 1));

    for (i = len_a - 1; i >= 0; i--)
    {
        carry1 = carry2;
        carry2 = (a[i] + (i - len_a + len_b >= 0 ? b[i - len_a + len_b] : '0') - 2 * '0' + carry1) / 10;
        result[i + 1] = (a[i] + (i - len_a + len_b >= 0 ? b[i - len_a + len_b] : '0') - 2 * '0' + carry1) % 10 + '0';//这里有问题
    }
    result[0] = carry1;
    result[len_a] = '\0';

    //去掉最前面无意义的0
    for (i = 0; result[i] == '0'; i++);
    for (j = 0; result[i]; i++, j++)
        result[j] = result[i];
    if (j == 0)
        result[j++] = '0';
    result[j] = '\0';

    return result;
}

程序代码：

char *add(const char *a, const char *b)
{
    size_t len_a = strlen(a), len_b = strlen(b), len_result = len_a > len_b ? len_a + 1 : len_b + 1;
    unsigned i, j;
    unsigned m, n;
    unsigned carry1 = 0, carry2 = 0;
    unsigned k_i = 1, k_j = 1;//k_i或k_j为0说明a或b已经读完

    char *result = (char *)malloc(sizeof(char) * (len_result + 1));

    i = len_a - 1;
    j = len_b - 1;
    result[len_result] = '\0';
    do
    {
        m = k_i ? a[i] : '0';
        n = k_j ? b[j] : '0';
        carry1 = carry2;
        carry2 = (m + n - 2 * '0' + carry1) / 10;
        result[len_a > len_b ? i + 1 : j + 1] = (m + n - 2 * '0' + carry1) % 10 + '0';
        i ? i-- : (k_i = 0);
        j ? j-- : (k_j = 0);
    } while (k_i || k_j);//直到两个数都读完结束循环
    result[0] = carry2 + '0';

    for (i = 0; result[i] == '0'; i++);
    if (i)
        for (j = 0; result[i - 1]; i++, j++)
            result[j] = result[i];

    return result;
}

[此贴子已经被作者于2018-12-21 17:39编辑过]