In a population, the birth rate is the percentage increase of the population due

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:
%u2022 The starting size of a population (minimum 2)
%u2022 The annual birth rate
%u2022 The annual death rate
%u2022 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.

Explanation / Answer

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#include <iostream>
using namespace std;
double getNewPopulation(double,double,double);
int main()
{int years,i;
double start,birthRate, deathRate, newPop;
cout<<"Enter the starting size of a population(minimum 2): ";
    cin>>start;
    while(start<2)
       {cout<<"Invalid entry ";
       cout<<"Enter the starting size of a population(minimum 2): ";
       cin>>start;
       }
    cout<<"Enter the annual birth rate: ";
    cin>>birthRate;
    cout<<"Enter the annual death rate: ";
    cin>>deathRate;
    cout<<"Enter the number of years to display(minimum 1): ";
    cin>>years;
    while(years<1)
       {cout<<"Invalid entry ";
       cout<<"Enter the number of years to display(minimum 1): ";
       cin>>years;
       }
cout<<" starting ending year population population ";
for(i=0;i<years;i++)
    {newPop=getNewPopulation(start,birthRate,deathRate);
     cout<<i+1<<" "<<start<<" "<<newPop<<endl;
     start=newPop;
     }
system("pause");
    return 0;
}
double getNewPopulation(double P,double B,double D)
{return P*(1. + B)*(1. - D);
}

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