Wavelength and Axial Mode Calculation in C++

#include // identifiers voiddisplayMenu(); doublecalculateWavelength(double f, double c); doublecalculateFirstAxialRoomMode(double c, double L); doublecalculateLitresPer100Km(double mpg); intmain() { // helper variables int option; double frequency, speed; double length; double mpg; // star main program while (true) { displayMenu(); std::cin>> option; if (option >=1&& option <=4) // valid option { if (option ==1) // calculate wavelength { std::cout<<"Please enter the frequency (Hz): "; std::cin>> frequency; std::cout<<"Please enter the speed (m/s): "; std::cin>> speed; double w =calculateWavelength(frequency, speed); std::cout<<"The wavelength is: "<< w <<" mts."<< std::endl; } elseif (option ==2) // calculate first axial room mode { std::cout<<"Please enter the speed of sound (m/s): "; std::cin>> speed; std::cout<<"Please enter the distance between boundary surfaces (mts): "; std::cin>> length; double f1 =calculateFirstAxialRoomMode(speed, length); std::cout<<"The first axial mode frequency is: "<< f1 <<" Hz."<> mpg; double lts_per_100km = calculateLitresPer100Km(mpg); std::cout<<"The amount of "<< mpg <<" (m/g) equals to "<< lts_per_100km <<" (lts/100km)."<