较简单的高精度题，但要判断大小。

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
int a[100010],b[100010],c[100010];
bool lower(string A,string B){
    if (A.size()<B.size()){
        return true;
    }else{
        return A.size()==B.size()&&A.compare(B)<0;
    }
    return false;
}
int main(){
    freopen("subtraction.in","r",stdin);
    freopen("subtraction.out","w",stdout);
	string A,B;
	cin>>A>>B;
	bool is=0;
	int len=max(A.size(),B.size());
	if (lower(A,B)){
		swap(A,B);
		is=1;
	}
	for (int i=A.size()-1,j=0;i>=0;i--,j++){
		a[j]=A[i]-'0';
	}
	for (int i=B.size()-1,j=0;i>=0;i--,j++){
		b[j]=B[i]-'0';
	}
	
	for (int i=0;i<len;i++){
		c[i]+=a[i]-b[i];
		if (c[i]<0){
			c[i+1]--;
			c[i]+=10;
		}
	}
	for (int i=0;i<100010;i++){
		c[i+1]+=c[i]/10;
		c[i]%=10;
	}
	for (;!c[len-1];){
		len--;
	}
	if (is==1){
		cout<<'-';
	}
	bool r=0;
	for (int i=len-1;i>=0;i--){
		cout<<c[i];
		r=1;
	}
	if (!r) cout<<0; 
	return 0;
}