Answer to Question #55227 in C++ for kklljj

Question

In a population, the birth rate is the percentage increase of the population due to births,
and the death rate is the percentage decrease of the population due to deaths. Write a
program that asks for the following: The starting size of a population (minimum 2) The annual birth rate The annual death rate。 The number of years to display (minimum 1) The program should then display the starting population and the projected population at the end of each year. It should use a function that calculates and returns the projected new size of the population after a year. The formula is N = P(1 + B)(1 - D) where N is the new population size, P is the previous population size, B is the birth rate, and D is the death rate. Annual birth rate and death rate are the typical number of births and deaths in a year per 1000 people, expressed as a decimal. So, for example, if there are normally about 32 births and 26 deaths per 1000 people in a given population, the birth rate would be .032 and the death rate would be .026.

Answer 1

#include <iostream>

using namespace std;

double prejected_population(double curr_population, double birth_rate, double death_rate);
int main()
{
double population;
double birth_rate;
double death_rate;
int years_to_display;
cout << "Enter current population (minimum 2): ";
cin >> population;
while (population < 2.0)
{
cout << "Wrong value of population (minimum 2)\nTry again: ";
cin >> population;
}
cout << "Enter birth rate ( from (0;1) ): ";
cin >> birth_rate;
cout << "Enter death_rate ( from (0;1) ): ";
cin >> death_rate;
cout << "Enter number of years to display (minimum 1): ";
cin >> years_to_display;
while (years_to_display < 1.0)
{
cout << "Wrong value of years (minimum 1)\nTry again: ";
cin >> population;
}
for (int i = 1; i <= years_to_display; ++i)
{
population = prejected_population(population, birth_rate, death_rate);
cout << "New size of population after " << i << " year(s) is " << population << endl;
}
system("pause");
return 0;
}

double prejected_population(double curr_population, double birth_rate, double death_rate)
{
return curr_population * (1 + birth_rate) * (1 - death_rate);
}