std::function Callbacks

Lab C++ Intermediate 20 points

Build a map<string, function<long long(long long, long long)>> for add, sub, mul, pow. Read op a b lines and print results or unknown.

Input

n, then n lines.

Output

n lines.

Example

Input

5
add 2 3
mul 4 5
pow 2 10
sub 1 9
mod 7 2

Output

5
20
1024
-8
unknown

Sample input available Sample output available

Editor

C++

Hints

std::function can hold any callable with the right signature.

Solution explanation

A dispatch table of functions replaces a long if/else chain.

Show solution

#include <iostream>
#include <functional>
#include <map>
#include <string>
using namespace std;

int main() {
    map<string, function<long long(long long, long long)>> ops = {
        {"add", [](long long a, long long b) { return a + b; }},
        {"sub", [](long long a, long long b) { return a - b; }},
        {"mul", [](long long a, long long b) { return a * b; }},
        {"pow", [](long long a, long long b) {
            long long r = 1;
            for (long long i = 0; i < b; i++) r *= a;
            return r;
        }},
    };
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        string op;
        long long a, b;
        cin >> op >> a >> b;
        auto it = ops.find(op);
        if (it == ops.end()) cout << "unknown\n";
        else cout << it->second(a, b) << "\n";
    }
    return 0;
}

Output

Answer