42.txt

#include<iostream>
#include<sstream>
#include<vector>
#include<string>
using namespace std;
string decimal(int,int);
string Int_to_String(int n)
{
ostringstream stream;
stream<<n;
return stream.str();
}
int main() {
    int N,D;
    cin>>N>>D;
    int integer = N/D;
    cout<<integer<<"."<<decimal(N%D,D)<<endl;
    return 0;
}

string decimal(int n,int d) {
    if(n == 0)
        return "0";
    vector<int> loop;
    vector<int> quotient;
    loop.push_back(n);
    int remainder;
    bool flag = false;
    int pos;    // 记录循环体开始位置，加（
    do {
        remainder = n*10%d;
        int i = 0;
        for(;i<loop.size();i++) {
            if(remainder == loop[i]) {
                pos = i;
                break;
            }
        }
        if(i != loop.size()) {
            flag = true;
            quotient.push_back(n*10/d);
            break;
        }
        loop.push_back(remainder);
        quotient.push_back(n*10/d);
        n = remainder;
    } while(n != 0);
    string s = "";
    for(int i=0;i<pos;i++) {
        s += Int_to_String(quotient[i]);
    }
    if(flag) {
        s += "(";
    }
    for(int i=pos;i<quotient.size();i++) {
        s += Int_to_String(quotient[i]);
    }
    if(flag) {
        s += ")";
    }
    return s;
}