大整数减法

#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int maxn = 2000;
int a[maxn];
int b[maxn];
int c[maxn];
char s[maxn];
char t[maxn];
char n[maxn];
int main(void)
{
    cin>>s>>t;
    int lens = strlen(s);
    int lent = strlen(t);
    if(lens<lent||lens==lent&&strcmp(s,t)<0)
    {
        strcpy(n,s);
        strcpy(s,t);
        strcpy(t,n);
        cout<<"-";
    }
    lens = strlen(s);
    lent = strlen(t);
    for(int i = 0; i < lens; i++)
        a[lens-i] = s[i]-‘0‘;
    for(int i = 0; i < lent; i++)
        b[lent-i] = t[i]-‘0‘;
    int lenc = 1;
    while(lenc<=lens||lenc<=lent)
    {
        if(a[lenc]<b[lenc])
        {
            a[lenc] += 10;
            a[lenc+1]--;
        }
        c[lenc] = a[lenc]-b[lenc];
        lenc++;
    } 
    while(c[lenc]==0)
        lenc--;
    for(int i = lenc; i >= 1; i--)
        cout<<c[i];
    cout<<endl;
    return 0;
}