大数相减运算

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

#define M 10005
int main()
{
    char *a, *b, ai[M], bi[M]; //
    int a1[M], b1[M], i, j, m, n, k, max;
    /////////////////
    //
    scanf("%s%s", ai, bi);
   
    a = ai;
    b = bi;

    if(strcmp(ai, bi) < 0)
    {
        a = bi;
        b = ai;
        printf("-");
    }

    k = m = strlen(a);
    n = strlen(b);
    if(k < n)
        k = n;        //选出最大位数是多少位

    /////////////////

    for(i = 0; i < m; i++)  //将字符串转换为数组
        a1[i] = a[m - 1 - i] - '0';

    for(j = 0; j < n; j++)
        b1[j] = b[n - 1 - j] - '0';

    i = 0;

    if(k == m)
    {

        for(j = 0; j < k; j++)
        {
            if(a1[i] < b1[j])
            {
                a1[i] = a1[i] - b1[j] + 10;
                a1[i + 1]--;
                i++;
            }
            else
            {
                a1[i] = a1[i] - b1[j];
                i++;
            }

        }

        i = k;

        while(a1[i] == 0)
            i--;

        if(i < 0)
            printf("0\n");

        else
        {
            for(; i >= 0; i--)
                printf("%d", a1[i]);

        }
    }
    else
    {
        for(j = 0; j < k; j++)
        {
            if(b1[i] < a1[j])
            {
                b1[i] = b1[i] - a1[j] + 10;
                b1[i + 1]--;
                i++;
            }
            else
            {
                b1[i] = b1[i] - a1[j];
                i++;
            }

        }

        i = k;

        while(b1[i] == 0)
            i--;

        if(i < 0)
            printf("0\n");
        else
        {
            for(; i >= 0; i--)
                printf("%d", b1[i]); ////

        }
    }

    return 0;
}