First c++ program. Convert fahrenheit to celsius and reverse

#include <iostream>

using namespace std;

//Fahrenheit-Celcius
//Convert Fahrenheit to Celsius and vice-versa
//Simple menu to choose conversion and stop or run again


void runMenu();
char userInteraction();
void displayResults(char menuChoice);
double calcFahrtoCel(double fahrValue);
double calcCeltoFahr(double celValue);


int main()
{
    runMenu();
}


// Run the program, then ask to run it again
void runMenu()
{
    displayResults(userInteraction());

    char runAgain = 'n';
    cout << "Would you like to do another conversion? (y or n)" << endl;
    cin >> runAgain;

    switch(runAgain)
    {
        case 'y':
        case 'Y':
        runMenu();
        break;

        default:
        break;
    }
}


// Ask which conversion: c-f or f-c. Return char f or c
char userInteraction()
{
    char menuChoice = 'x';

    cout << "Convert Fahrenheit to Celsius or Celsius to Fahrenheit" << endl;
    cout << "Press f for Fahrenheit to Celsius" << endl;
    cout << "Press c for Celsius to Fahrenheit" << endl;
    cin >> menuChoice;

    return menuChoice;
}


// Take input for conversion, then run calculation
void displayResults(char menuChoice)
{
    double fahrInput = 0.0;
    double celInput = 0.0;

    switch(menuChoice)
    {
        case 'f':
        case 'F':
            cout << "Enter Fahrenheit value: " << endl;
            cin >> fahrInput;
            cout << fahrInput << " Fahrenheit = "
                 << calcFahrtoCel(fahrInput) << " Celsius" << endl;
            break;

        case 'c':
        case 'C':
            cout << "Enter Celsius value: " << endl;
            cin >> celInput;
            cout << celInput << " Celsius = "
                 << calcCeltoFahr(celInput) << " Fahrenheit" << endl;
            break;

        default:
            cout << "Illegal option. Please press only f or c" << endl;
    }
}


// Calculate Fahrenheit to Celsius
double calcFahrtoCel(double fahrValue)
{
    double celValue = (fahrValue-32.0)*(5.0/9.0);
    return celValue;
}


// Calculate Celsius to Fahrenheit
double calcCeltoFahr(double celValue)
{
    double fahrValue = celValue*(9.0/5.0)+32.0;
    return fahrValue;
}