add even (or odd) numbers from input

[cynthann]

Hello
Please help. I am having a hard time making the leap from where I am to then picking out numbers (in this instance adding even numbers). Any suggestions or pointers would be greatly appreciated.

#include <iostream>
using namespace std;
// program computes the sum of all even numbers from input number

int compute_sum(int n);
int main()
{
int n;

cout << "enter a number" << endl;

cin >> n;

if (n % 2 == 0)
cout <<"even "<<compute_sum(n)<< endl;

else
cout << "odd " << endl;

return 0;
// return ((n  & 1) == 1); // odd
// return ((n & 1) == 0);  // even
}

int compute_sum(int n)
{
int count = 1;
int sum = 0;
        while (count <= n)
                {
                  sum = sum + count;
                  count = count + 1;
                }
           return sum;
}

[WolfPack]

// program computes the sum of all even numbers from input number

This part of the objective does not make sense to me. Care giving a sample input number, like 12, and explaining what the expected result would be?
Right now it gives the result

1 + 2 + 3 + ... + 11 + 12  = 78

for the input of 12.

[cynthann]

So, if you input 12 it would add

2 + 4 + 6 + 8 + 10 + 12

[WolfPack]

You can do that by just changing these lines.I am not giving you the answer because if you wrote the above program yourself, you can surely do this part using the hint I have given you.

count = 1;
count = count + 1;

[cynthann]

duh! Thank you for your help. You know when you have been sitting in front of something for so long that the screen begins to melt?

count = 2;
count = count + 2;

[Bench]

I can think of a better way. if you wish to calculate the sum of all numbers in a range, the formula is n( (First+Last)/2 ) in your case, the first number is always going to be 2 ... 'n' is the "number of numbers" in the range.. eg, from 2-to-12, n=6 ... or 2-to-100, n=50... or 2-to-10000, n=5000.. (see a pattern there?)

[ruhneb03]

Hi cynthann,

Can you give me the complete working program of that if you get it right? Thanks.