算法笔记-----大整数相乘---数组实现

//
// Created by alim on 2017/12/18.
//

#include "dazs.h"
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define NUM_LEN   50//数字的最大长度

int main()
{
    int i, n, temp = 0, p, k;

    char num1[NUM_LEN], num2[NUM_LEN];
    puts("Please input the first number:");
    gets(num1);
    puts("\nPlease input the second number:");
    gets(num2);
    int len1 = strlen(num1);
    int len2 = strlen(num2);
    int *arr1 = (int *)malloc(sizeof(int) * len1);
    int *arr2 = (int *)malloc(sizeof(int) * len2);

    for(i = 0; i < len1; i++)
    {
        arr1[i] = (int)num1[i] - 48;   //把字符转换成对应的整数
    }
    for(i = 0; i < len2; i++)
    {
        arr2[i] = (int)num2[i] - 48;
    }

    int *result = (int *)malloc(sizeof(int) * (len1 + len2));
    n = len1 + len2 - 1;
    for(i = 0; i <= n; i++)
    {
        result[i] = 0;   //初始化结果数组
    }

    for(i = len1 - 1; i >= 0; i--)
    {
        p = arr1[i];
        for(k = len2 - 1; k >= 0; k--)
        {
            temp = result[n] + p * arr2[k];
            if(temp >= 10)   //如果temp>=10，则应该进位
            {
                result[n] = temp%10;   //取个位
                result[n - 1] += temp/10;   //向前进位
            }
            else
            {
                result[n] = temp;
            }
            n--;
        }
        n = n + len2 - 1;   //回退 len2 - 1 位
    }

    //输出计算结果
    puts("\nThe calulation results is:");
    if(result[0] != 0)
    {
        printf("%d",result[0]);
    }
    for(i = 1; i <= len1 +len2 -1; i++)
    {
        printf("%d", result[i]);
    }
    printf("\n\n");
    return 0;
}