关于string类型的大小写转换函数

对于string类型的有力工具

transform(s.begin(), s.end(), s.begin(),::tolower)大写转小写
transform(s.begin(), s.end(), s.begin(),::toupper)小写转大写

样例 洛谷P2264

#include<bits/stdc++.h>
using namespace std;

const int N = 1000;
int n; string str[N];
map<string, bool> mp;

int main(){
	cin >> n;
	for(int i = 1; i <= n; i ++){
		string s; cin >> s;
		transform(s.begin(), s.end(), s.begin(),::tolower);
		mp[s] = 1;
	}
	char c;
	int ans = 0, cnt = 0;
	string s = "";
	while(~scanf("%c", &c)){
		if(c >= 'a' && c <= 'z') s += c;
		else if(c >= 'A' && c <= 'Z') s += c;
		else{
			transform(s.begin(), s.end(), s.begin(),::tolower);
			cout << s << endl;
			if(mp[s] == 1)	ans ++, cnt ++, str[cnt] = s;
			mp[s] = 0;
			s = "";
		}
		if(c == '.'){
			for(int i = 1; i <= cnt; i ++){
				mp[str[i]] = 1; str[i] = "";
			}
			cnt = 0;
		}
	}
	cout << ans << endl;
	return 0; 
}