两个大数计算

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main()
{
    char a[10050];
    char b[10050];
    char sum[10051];
    while(scanf("%s",a)!=EOF)
    {
        int flag =0;
        scanf("%s",b);
        int lena,lenb;
        lena = strlen(a);
        lenb = strlen(b);
        if(lena<lenb)
        {
            char tmp[10050];
            int tmpn;
            for(int i =0;i<lenb;i++)
            {
                tmp[i] = b[i];
                b[i] = a[i];
                a[i] = tmp[i];
            }
            tmpn = lenb;
            lenb = lena;
            lena = tmpn;
        }//将长的数组存在a数组中
        if(lena!=lenb)//将两个数组对齐
        {
            int k =lena-lenb;//补k个零
            for(int i =lena-1;i>=k;i--)
            {
                b[i]=b[i-k];
            }
            for(int i =0;i<k;i++)
            {
                b[i] ='0';
            }
        }
        for(int i=lena;i>0;i--)
        {
            if(a[i-1]+b[i-1]-'0'+flag>'9')
            {
                sum[i] = a[i-1]+b[i-1]-'0'+flag-10;
                flag =1;
            }
            else
            {
                sum[i] = a[i-1]+b[i-1]-'0'+flag;
                flag = 0;
            }
        }
        if(flag==1)
        {
            sum[0] = '1';
        }
        if(sum[0]!=0)
        {
            printf("%c",sum[0]);
        }
        for(int i=1;i<=lena;i++)
        {
            
            printf("%c",sum[i]);
        }
        printf("\n");
    }
    return 0;
}