Homework error?

[halamaker]

For an assignment I'm supposed to make a program that calculates the even numbers between 1 and a user defined 'n.' The program is supposed to continue until the user wants it to stop with an entry of '0'. I thought all was well and good it seemed to be working fine but if I keep entering test cases it screws up. For example if I enter 16, 21, and 42 the answers will be correct. But if after 42 I enter a lower number like say 12, it will just continue to produce 42's answer until I enter a number higher than 42. Where did I go wrong? Thanks so much for any and all help!

#include <iostream>
using namespace std;

int main()
{
    int sum = 0;  
    int n = 0; 
    int j = n%2; 
	
    cout << "Please enter an integer [0 to stop]: " ;
	cin >> n ;
    
    while (n > 0)
    {    
          while (j <= n)  
          {
          sum = sum + j ;
          j = j + 2 ;    
          }

          cout << "The sum of the even numbers between 1 and " << n  << " is " << sum << endl ; 
          cout << "Please enter an integer [0 to stop]: " ;
          cin >> n ;
    }

	system("pause");
	return 0;
}

[MiiNiPaa]

You never modify j after you done with it and got a new n

[jlb]

What is the purpose of line 8? Since n is zero won't j always be zero? Maybe you need to do this test elsewhere, maybe in the loop?

[halamaker]

MiiNiPaa - I'm sorry to be daft, but in what way am I to modify j?

jlb - j changes according to what the user enters for n. If the user enters an even integer, j should = 0 and if the user enters an odd integer j should = 1. (At least that's how my professor described it)

[jlb]

But you calculate this value before the user enters anything. Shouldn't the calculation be done after you get your user input?

[halamaker]

Ok, I altered the code a bit with your suggestion but I'm still getting errors, it will calculate even numbers correctly but not odd numbers. I should get the answer 110 for the sum of all even numbers between 1 and 21, but I get 121 instead. Here is my updated code:

Edit: I attempted changing int j = n%2 to int j = 0, but that made everything weird and lower numbers than the number previously entered would equal 0...

#include <iostream>
using namespace std;

int main()
{
	int sum = 0;  
    int n = 0; 
    int j = n%2; 
	
    cout << "Please enter an integer [0 to stop]: ";
	cin >> n ;
    
    while (n != 0)
    { 
          int sum = 0; 
          j = n%2;
          while (j <= n)  
          {
          sum = sum + j ;
          j = j + 2 ;    
          }

          cout << "The sum of the even numbers between 1 and " << n  << " is " << sum << endl ; 
          cout << "Please enter an integer [0 to stop]: " ;
          cin >> n ;
    }

	system("pause");
	return 0;
}

[halamaker]

Solved I figured it out, thank you so much!!!