void functions

[Frausty]

For my c++ class we are to find the coast altitude and burnout altitude of two rockets. We are required to use the specific function prototype. I have been looking for help, but it seems most examples with void functions do not contain parameters. The section before the main cannot be changed. help is much appreciated.

  // Include Section
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

// This funtion computes the burnout altitude and the
// coast altitude of a model rocket.
// The first 6 parameter are the input data
// to the function. Parameter 7 and 8 return the results
void computeA( double massR,	//Rocket Mass (g)
			   double massE,	//Engine Mass (g)
			   double massP,	//Propellant Mass (g)
			   double dia,		//Diameter of Rocket (mm)
			   double advTh,	//Adv thrust of Engine (N)
			   double burnD,	//Burn Duration (s)
			   double& altB,	//Burnout Altitude (m)
			   double& altC);	//Coast Altitude (m)

// Main Program
int main( )
{
	// Constant Declarations
	const double a = 9.8;
	const double pi = 3.14;
	// Character Declarations
	char runAgain;
	// Variable Declarations
	double massR;	//Rocket Mass (g)
	double massE;	//Engine Mass (g)
	double massP;	//Propellant Mass (g)
	double dia;		//Diameter of Rocket (mm)
	double advTh;	//Adv thrust of Engine (N)
	double burnD;	//Burn Duration (s)
	double altB;	//Burnout Altitude (m)
	double altC;	//Coast Altitude (m)
	double liftoffMass;
	double coastPhaseMass;
	double avgMass;
	double k;
	double A;
	double burnVel;

	// Output Identification
	cout << "Take Home #8 - Rocket Altitudes. \n\n";
	do
	{
	cout << " Enter the mass of the rocket in grams: ";
	cin >> massR;
	cout << " Enter the mass of the engine in grams: ";
	cin >> massE;
	cout << " Enter the mass of the propellant in grams: ";
	cin >> massP;
	cout << " Enter the diameter of the rocket in meters: ";
	cin >> dia;
	cout << " Enter the average thrust of the engine in newtons: ";
	cin >> advTh;
	cout << "Enter the burn duration of the engine in seconds: ";
	cin >> burnD;
	computeA( massR, massE, massP, dia, advTh, burnD, altB, altC);

	 A=pi*(dia/4000);
	 k=.05*1.2*0.75*A;
	 liftoffMass = (massR/1000) + (massE/1000);							// liftoff mass of the vehicle
	 coastPhaseMass = (massR/1000) + (massE/1000) - (massP/1000);		// mass during the coast phase
	 avgMass = (liftoffMass + coastPhaseMass) / 2;					// average mass during the boost phase
	 burnVel = sqrt((advTh-avgMass*a)/k)*tanh((burnD/avgMass)*sqrt(k*(advTh-avgMass*a)));
	
	cout << "\n The burnout altitude is " << altB << " meters.\n";
	cout << " The coast altitude is " << altC << " meters.\n";
	cout << " Do you want to run the program again? (y or n): ";
	cin >> runAgain;
	cout << "\n";
	}
	while (runAgain == 'y');
	return 0;
}
void computeA( double massR,	
			   double massE,
			   double massP,
			   double dia,	
			   double advTh,
			   double burnD,
			   double& altB,
			   double& altC)
{
	const double a = 9.8;
	double k;
	double avgMass;
	double coastPhaseMass;
	double burnVel;
	 altB = (avgMass/k)*log(cosh((burnD/avgMass)*sqrt(k*(advTh-avgMass*a))));
	 altC = (coastPhaseMass/(2*k))*log(((k*(burnVel*burnVel))/(coastPhaseMass*a))+1);
}
	
	

[keskiverto]

You have the input data on lines 78-83.
You have equations on lines 92-93 that produce the results.

You do lack the equations that define the variables on lines 88-91 from the input data.
How do you calculate k, avgMass, coastPhaseMass, burnVel? If your answer is: "Look at lines 63-67", then the response is: "The body of computeA does not know anything about main. It only has input data and its own equations." So make it have what it has to have (and strip from main() everything non-essential).

[Frausty]

So, all of the equations should be in the void section at the end. Then I must define variables 88-91 in the void function at the beginning?

[Frausty]

Thank you keskiverto. i got it.

[giblit]

Its just a function not a void function. Void is the return type.