Calculate fuel efficiency

/*
Author: Wilton Marranzini
Objective: Program calculates the fule effiency of the car on the trip in
miles/gallon and the cost for gasoline at the end of the trip.
*/

#include <iostream.h>           //including lib.
#include <math.h>             //including lib.
#include <cstring.h>           //including lib.
                     //Prototypes functions
void description();            //Description cout fuction.
float full_efficiency(int miles, int gallons);//efficiency function.
float cost(float price, int gallons);   //Cost function.
int main()                //Main Function
{ string gas_station;          //String for gas station name.
  int num_miles;             // Variable for number of miles
  int num_gallons;            //Variable for number of gallons.
  float price_per_gallons;        //Variable for price per gallons.
  float efficiency;           //variable for efficiency.
  float cos;               //variable for cost
  int a;                 //keeps screen function
  description();             //Discription function
  cout<< "Enter gas station name\n";
  getline(cin, gas_station);       //Getting gas station title
  cout<< "Name of gas station Is " << gas_station <<".\n";
  cout<<endl;
  cout<< "Enter the numbers of miles travel.\n";
  cin>>num_miles;//storing numbers of miles
  cout<< "Enter the number of gallons of gasoline purchased.\n";
  cin>>num_gallons;//storing number of gallons
  cout<< "Enter the Price per gallons.\n";
  cin>>price_per_gallons;        //storing price per gallons
  efficiency = full_efficiency(num_miles,num_gallons);//calling function.
  cos =cost(price_per_gallons,num_gallons);//calling function.
  cout<<"The efficiency is "<<efficiency<<" for "
    <<num_miles<<" miles per number of "<<num_gallons<<" gallons\n";
  cout<<"Gallons used on the trip is "<<num_gallons<<" The cost of the trip "
    <<"is "<<"$"<< cos <<endl;
  cin>>a;               //keeps screen open
  return 0;              //returning value
}
void description()
{
	cout<< "Program calculates the fule effiency of the car on the trip\n"
  	 << "in miles/gallon and the cost for gasoline at the end of the\n"
    << "trip.\n";
}
float full_efficiency(int miles, int gallons)
{
	float efficien;           //efficiency variable
	efficien = miles/gallons;
	return (efficien);          //returning value
}
float cost(float price, int gallons)
{
	float charge;            //charge variable
  charge = price*gallons;
  return (charge);           //returning value
}