大数相加算法的C代码

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

#define max(a,b) (a)>(b)?(a):(b)

int big_add(char*,char*,char*);
int big_sub(char*,char*,char*);
int big_compare(char*,char*,int*);
int is_number_string(char*);
 
int main()
{
    char num1[80],num2[80],num3[100];

    puts("First number:");
    gets(num1);
    puts("Second number:");
    gets(num2);
    if(big_add(num1,num2,num3))
    {
        puts("Sum:");
        puts(num3);
        big_sub(num1,num2,num3);
        puts("Difference::");
        puts(num3);
    }
    else
        puts("Input error!");

    return 0 ;
}

int big_add(char *num1,char *num2, char *sum)
{
    if(is_number_string(num1)&&is_number_string(num2))
    {
        int len1=strlen(num1),len2=strlen(num2),c=0;
        int len=max(len1,len2)+1;
        char *res=(char*)malloc((len+1)*sizeof(char));

        memset(res,0x30,len*sizeof(char));
        res[len]=0;

        for(;len>0;len1--,len2--)
        {
            len--;

            len1>0&&(res[len]+=num1[len1-1]-0x30);
            len2>0&&(res[len]+=num2[len2-1]-0x30);
            res[len]+=c;

            if(res[len]>0x39)
            {
                res[len]-=0xa;
                c=1;
            }
            else
                c=0;
        }

        res[len]+=c;

        while(!(*res-0x30))
            res++;

        strcpy(sum,res);

        return(1);
    }
    return(0);
}

int big_sub(char *num1,char *num2,char *diff)
{
    if(is_number_string(num1)&&is_number_string(num2))
    {
        int com;

        big_compare(num1,num2,&com);

        if(com>0)
        {
            int len1=strlen(num1),len2=strlen(num2),c=0;
            int len=max(len1,len2)+1;
            char *res=(char*)malloc((len+1)*sizeof(char));

            memset(res,0x30,len*sizeof(char));
            res[len]=0;

            for(;len>0;len1--,len2--)
            {
                len--;

                len1>0&&(res[len]+=num1[len1-1]-0x30);
                len2>0&&(res[len]-=num2[len2-1]-0x30);
                res[len]-=c;

                if(res[len]<0x30)
                {
                    res[len]+=0xa;
                    c=1;
                }
                else
                    c=0;
            }

            res[len]+=c;

            while(!(*res-0x30))
                res++;

            strcpy(diff,res);
        }
        else
        {
            *diff='-';

            big_sub(num2,num1,diff+1);
        }

        return(1);
    }
    else
        return(0);
}

int big_compare(char *num1,char *num2,int *result)
{
    if(is_number_string(num1)&&is_number_string(num2))
    {
        int len1=strlen(num1),len2=strlen(num2);

        if(len1==len2)
        {
            while(*num1++==*num2++);
            
            *result=*num1-*num2;
        }
        else
            *result=len1-len2;

        return(1);
    }
    else
        return(0);
}

int is_number_string(char *str)
{
    for(;*str;str++)
        if(*str<'0'||*str>'9')
            return(0);

    return(1);
}