# Sum of all even integers? Help?

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• 04-03-2013, 02:59 AM
psx2514
Sum of all even integers? Help?
The assignment says, "Design and implement and application that reads an integer value and prints the sum of all even integers between 2 and the input value, inclusive. Print an error message if the input value is less than 2. Prompt accordingly." Okay. I don't understand exactly what they want. Do they want the output to be the sum of all the numbers between 2 and the inputted number, so for instance if the user enters 10, the output would be 30 because 2+4+6+8+10 = 30. Or do they want you to have the output list all of the even numbers between two and the inputted number (inclusive), so that the output is 2, 4, 6, 8, 10...? I know you can two the second option with a for loop, but could someone steer me in the right direction on how to do the first option (if that's what it's asking for)? Thanks!
• 04-03-2013, 03:05 AM
Norm
Re: Sum of all even integers? Help?
Quote:

prints the sum ...
I think the requirement is the sum.
Quote:

how to do the first option
Define a variable to hold the sum
write a loop
add the even numbers to the sum
end loop
print the sum
• 04-03-2013, 03:05 AM
psx2514
Re: Sum of all even integers? Help?
Nevermind. I got it. A for loop is the best way to do it, right?
• 04-03-2013, 03:05 AM
pbrockway2
Re: Sum of all even integers? Help?
You are supposed to print "the sum of all even integers" ie 30.

If you know how to list the even numbers in a for loop, try using the for loop but instead of printing the numbers add them to some variable like total. After the loop finishes total should contain he desired sum.

 Yes
• 04-03-2013, 03:08 AM
wsaryada
Re: Sum of all even integers? Help?
I believe they want the first option, print the sum of all event integer. And you can also do it using a for-loop if you want to. Or any other loop statement will be fine.
• 04-03-2013, 06:46 PM
jim829
Re: Sum of all even integers? Help?
Quote:

Originally Posted by psx2514
A for loop is the best way to do it, right?

Well, not really because it runs in linear time. But then it wouldn't be much of a programming exercise. Since you are working with integers, you can use the following to check your answer (assuming of course I didn't make a mistake).

Code:

```int n; // initialize to the top range of your series int k = n/2;  // the number of even numbers to sum. (k will be the same for n where n = 2r or 2r+1) int sum = k * (k + 1); // the sum of even numbers from 2 to n inclusive```
Regards,
Jim