Metric Converter(Simple Conditions)

#include <iostream>

using namespace std;

int main() {
    double distance;
    cin >> distance;
    cin.ignore();

    string inputMetric, outputMetric;
    cin >> inputMetric >> outputMetric;

    if (inputMetric == "m") {
        distance /= 1000;
    }
    else if (inputMetric == "cm") {
        distance /= 100000;
    }
    else if (inputMetric == "mm") {
        distance /= 1000000;
    }
    else if (inputMetric == "mi") {
        distance /= 0.621371192;
    }
    else if (inputMetric == "in") {
        distance /= 39370.0787;
    }
    else if (inputMetric == "ft") {
        distance /= 3280.8399;
    }
    else if (inputMetric == "yd") {
        distance /= 1093.6133;
    }

    if (outputMetric == "m") {
        distance *= 1000;
    }
    else if (outputMetric == "cm") {
        distance *= 100000;
    }
    else if (outputMetric == "mm") {
        distance *= 1000000;
    }
    else if (outputMetric == "mi") {
        distance *= 0.621371192;
    }
    else if (outputMetric == "in") {
        distance *= 39370.0787;
    }
    else if (outputMetric == "ft") {
        distance *= 3280.8399;
    }
    else if (outputMetric == "yd") {
        distance *= 1093.6133;
    }

    cout << distance << endl;
    return 0;
}

Решение с тернарен оператор:

#include <iostream>

using namespace std;

int main() {
    double distance;
    cin >> distance;
    cin.ignore();

    string inputMetric, outputMetric;
    cin >> inputMetric >> outputMetric;

    distance /=
        inputMetric == "m" ? 1000 :
        inputMetric == "cm" ? 100000 :
        inputMetric == "mm" ? 1000000 :
        inputMetric == "mi" ? 0.621371192 :
        inputMetric == "in" ? 39370.0787 :
        inputMetric == "ft" ? 3280.8399 :
        inputMetric == "yd" ? 1093.6133 : 1;

    distance *=
        outputMetric == "m" ? 1000 :
        outputMetric == "cm" ? 100000 :
        outputMetric == "mm" ? 1000000 :
        outputMetric == "mi" ? 0.621371192 :
        outputMetric == "in" ? 39370.0787 :
        outputMetric == "ft" ? 3280.8399 :
        outputMetric == "yd" ? 1093.6133 : 1;

    cout << distance << endl;
    return 0;
}

Решение с колекция:

#include <iostream>
#include <map>

using namespace std;

int main() {
    double distance;
    cin >> distance;
    cin.ignore();

    string inputMetric, outputMetric;
    cin >> inputMetric >> outputMetric;

    map <string, double> metricsToKM = {
        {"km", 1},
        {"m", 1000},
        {"cm", 100000},
        {"mm", 1000000},
        {"mi", 0.621371192},
        {"in", 39370.0787},
        {"ft", 3280.8399},
        {"yd", 1093.6133}
    };

    cout << distance / metricsToKM[inputMetric] * metricsToKM[outputMetric] << endl;
    return 0;
}