Snake Case

#include<iostream>
#include<cstdio>
using namespace std;

int main(){
    int t; cin >> t;
    while(t--){
        int n; cin >> n;
        char str[n+1];
        cin.ignore();
        gets(str);
        int i, j = 0, flag1 = 0, flag2 = 0;
        for(i = 0; i < n; i++){
            if(i == 0 && str[i] == ' ') {
                flag1 = 1;
                continue;
            }
            if(i == n-1 && str[i] == ' ') {
                flag2 = 1;
                continue;
            }
            if(str[i] == ' ' && i != 0) str[j++] = '_';
            else str[j++] = tolower(str[i]);
        }
        if(flag1) n--;
        if(flag2) n--;
        for(i = 0; i < n; i++){
            cout << str[i];
        }
        cout << endl;
    }
}