#include <iostream>
#include <iomanip>
using namespace std;

// Prototype for function getdata()
int getData(int&, int&, double&, double&);

// Prototype for function getPop()
double getPop(int start, double death, double birth);

// Function main
int main()
{
    // Variable declaration
    int years, startPop;
    double newPop;
    char x;
    double deathRate, birthRate;
    double totalPop;
    newPop = startPop + (birthRate * startPop) - (deathRate * startPop);
    
    // Get user input
    getData(startPop, years, deathRate, birthRate);        
    
    // Set accumulator
    totalPop = 0;
    
    // Perform calculations
    totalPop = getPop(startPop, deathRate, birthRate);
    
    // Display and Format output
    cout << fixed << showpoint << setprecision(1);
    cout << "The population increased from " << startPop << " to " << totalPop;
    
    // Pause script
    cout << "Press the enter key to exit the program." << endl;
    cin.ignore();
    cin.get(x);
    
    return 0;
}

int getData(int start, int year, double deaths, double births)
{
    cout << "What is the starting population?" << endl;
    cin >> start;
    // Validate startPop
    while (start < 2)
    {
          cout << "The starting population may not be less than two." << endl;
          cout << "Please enter a new starting population." << endl;
          cin >> start;
    }
    cout << "For how many years will the population change?" << endl;
    cin >> year;
    // Validate years
    while (year < 1)
    {
          cout << "Years may not be less than one." << endl;
          cout << "Please try again, entering a new value for years." << endl;
          cin >> year;
    }
    cout << "What is the death rate? Please enter the percentage in decimal form." << endl;
    cin >> deaths;
    // Validate death rate
    while (deaths < 0)
    {
          cout << "The death rate may not be negative.  Please enter a new death rate." << endl;
          cin >> deaths;
    }
    cout << "What is the birth rate? Please enter the percentage in decimal form." << endl;
    cin >> births;
    // Validate birth rate
    while (births < 0)
    {
          cout << "The birth rate may not be negative. Please enter a new birth rate." << endl;
          cin >> births;
    }
    return 0;
}

double getPop(int start, double death, double birth)
{
    int years;
    double newPop, totalPop;
    for (int count = 1; count <= years; count++)
    {
        newPop = start + (start * birth) - (start * death);
        totalPop += newPop;
    }
    return totalPop;
}