Destructor Order

Lab C++ Intermediate 20 points

Write class Tracer that prints +NAME when constructed and -NAME when destroyed. Read names and create one Tracer per name as local variables in nested blocks: the first name's object lives in the outermost block, the next in a block inside it, and so on (use recursion). Print end after everything is destroyed.

Input

n, then n names.

Output

The construction/destruction trace, then end.

Example

Input

3
A
B
C

Output

+A
+B
+C
-C
-B
-A
end

Sample input available Sample output available

Editor

C++

Hints

Local objects are destroyed in reverse order of creation, when their scope ends.

Solution explanation

Deterministic destruction is what makes RAII reliable in C++.

Show solution

#include <iostream>
#include <string>
#include <vector>
using namespace std;

class Tracer {
public:
    explicit Tracer(string name) : name_(name) { cout << "+" << name_ << "\n"; }
    ~Tracer() { cout << "-" << name_ << "\n"; }

private:
    string name_;
};

void nest(const vector<string> &names, size_t i) {
    if (i == names.size()) return;
    Tracer t(names[i]);
    nest(names, i + 1);
}

int main() {
    int n;
    cin >> n;
    vector<string> names(n);
    for (auto &s : names) cin >> s;
    nest(names, 0);
    cout << "end\n";
    return 0;
}

Output

Answer