NEed help with my homework. Almost complete

[iszitreal]

What can i change in my code to make this run accordingly? using VS2010.




The population of a town A is less than the population of town B. However, the population of town A is growing faster than the population of town B. Write a program that prompts the user to enter the population and growth rate of each town. The program outputs after how man years the population of town A will be greater than or equal to the population of town B and the populations of both the towns at the same time.


#include<iostream>
using namespace std;

int main()
{
double popA, popB, rateA, rateB, newpopA, newpopB;
int numOfYears = 0;

cout << "Enter population for town A: ";
cin >> popA;
cout << "Enter population for town B (Must be larger than town A): ";
cin >> popB;

if (popA < popB)
{
cout << "Enter the growing rate of town A: ";
cin >> rateA;
cout << "Now enter the growing rate of Town B: ";
cin >> rateB;

if (rateA <= rateB)
cout << "Invalid ";


else if (rateA > rateB)
{
while (newpopA < newpopB)

cout << "Population A: " << newpopA << endl;
newpopA = (popA * (rateA / 100.0)) + popA;

cout << "Population B: " << newpopB << endl;
newpopB = (popB * (rateB / 100.0)) + popB;
numOfYears++;

}
}
if (popA > popB)
cout << "Your input was invalid";
return 1;

}

[tipaye]

First of all, formatting the code would have given line numbers and made this easier :-(
Also, indentation!

Your while(newpopA < newpopB) needs an opening brace after it and a closing brace after numOfYears++

newpopA and newpopB are uninitialised, so there's a good chance your loop may never run, regardless of the values of popA and popB.

Even if the loop was working, you're never actually incrementing newpopA or newpopB, only assigning the same value to them everytime, plus omitting output of the final values.

Two rules you could have followed that would have saved you here:

Explicitly initialise all variables before use (maybe define them just before using, that would have helped too)
prefer int x = 0; to int x;

Always use braces to denote the block of if, while, for, do-while, etc. statements, even if the block is a single line or missing.
prefer

if (x > 0)
{
    do_something();
}

to

if (x > 0)
   do_something();

See suggested corrections below; I'm unsure of the actual growth algorithm, what you showed up there suggests you want to add the same percentage of the original population every year but I've chosen to just increase the current population by the same percentage every year, to highlight the ambiguity of the question.

#include<iostream>

using namespace std;

int main()
{
	double popA(0.0), popB(0.0);

	cout << "Enter population for town A: ";
	cin >> popA;

	cout << "Enter population for town B (Must be larger than town A): ";
	cin >> popB;

	if (popA < popB)
	{
		double rateA(0.0), rateB(0.0);

		cout << "Enter the growing rate of town A: ";
		cin >> rateA;

		cout << "Now enter the growing rate of Town B: ";
		cin >> rateB;

		if (rateA <= rateB)
		{
			cout << "Invalid ";
		}
		else
		{
			int numOfYears = 0;
			while (popA < popB)
			{
				popA += (popA * (rateA / 100.0));
				cout << "Population A: " << popA << endl;

				popB += (popB * (rateB / 100.0));
				cout << "Population B: " << popB << endl;

				cout << "after " << ++numOfYears << " years" << endl;
			}
		}
	}
	else
	{
		cout << "Your input was invalid";
	}

	return 1;
}