数制转换(一个任意进制的数转换为另一个进制的数)

#include<bits/stdc++.h>

using namespace std;
typedef long long ll;
vector<char> ve;

int main(){
	ll a,b;
	string n;
	while(cin>>a){
		ve.clear();
		cin>>n;
	
		cin>>b;
		ll len = n.size();
		ll sum = 0;
		ll res;
		for(int i=0;i<len;i++){
			if(n[i]>='A' && n[i]<='Z'){
				n[i] += 32;
			}
			if(n[i]>='0' && n[i]<='9') res =  (n[i]-'0');
			if(n[i]>='a' && n[i]<='z') res = (n[i]-'a'+10);
			sum = sum*a + res;
		}


		if(sum==0){
			cout<<"0"<<endl;
			continue;
		}
		while(sum!=0){
			res = sum % b;
			if(res <= 9) ve.push_back(res + '0');
			else ve.push_back(res-10+'A');
			sum /= b;
		}
		reverse(ve.begin(),ve.end());
		for(ll i=0;i<ve.size();i++){
			cout<<ve[i];
		}
		cout<<endl;
	}
	return 0;
}