# [C#] Sum of first x natural numbers

1. Jun 5, 2014

I am writing this in C#. Here is the code.
Code (Text):

using System;

namespace ConsoleApplication3
{
class Program
{
static void Main(string[] args)
{

int sum = 0;
int uservalue;
for (int i = 0;i <= uservalue;i++)
{
sum += i;
}
Console.WriteLine("Sum of the Natural numbers from 0 to {1} is:{0}",sum,uservalue);
}
}
}
Problems;
1. If I write 100 in the console, it assumes that I wrote 57
2. How do I make it possible for the user to write and calculate the sum as much as he/she wants? I wrote two Console.ReadLines there. So it allows me to write only one number, after getting that string, if I write another number, the console closes

Last edited: Jun 5, 2014
2. Jun 5, 2014

### Staff: Mentor

Have you checked docs? What does Console.Read() return?

No idea why 57, I would expect 49.

Then

$$\sum_{i=1}^n i= \frac {n(n+1)}2$$

3. Jun 5, 2014

Oh, I got it.
The code is now updated,but still, I don't know how to solve problem 2
Yes, I know this. However, I want to learn how to do it the long way

4. Jun 5, 2014

### Staff: Mentor

The most obvious approach - loop that ends on a particular input.

5. Jun 5, 2014

I have found something : While(true)
{

}
I put all my code into this and it's alright

I have noticed that large numbers return absurd results, for example, if I write 10000000, it returns -2004260032 . Absurd.

6. Jun 5, 2014

This is my code now
Code (Text):

using System;

namespace ConsoleApplication3
{
class Program
{
static void Main(string[] args)
{
int uservalue;
int sum = 0;
Console.WriteLine("Calculate the Sum of Natural numbers from 0 to your number");
Console.WriteLine("----");
while(true)
{
Console.Write("Enter Number:");
if(uservalue==0)
{
Console.WriteLine("Invalid Number");
}
else
{
for (int i = 0; i <= uservalue; i++)
{
sum += i;
}
Console.WriteLine("Sum of the Natural numbers from 0 to {1} is:{0}", sum, uservalue);
sum = 0;
}

}

}
}
}

7. Jun 5, 2014

### Staff: Mentor

What are limits to the value that can be stored in a signed, 32 bit int?

8. Jun 5, 2014

$2^{32}\text{ Which is equal to }4294967296$

9. Jun 5, 2014

### Staff: Mentor

Your "while(true)" loop is an "infinite loop", that is, you presumably have to do something like control-C to abort it when you don't want to find any more sums. You might want to consider how to end the program more "gracefully" from the user's point of view.

10. Jun 5, 2014

### Staff: Mentor

That's actually wrong, you missed the "signed" part, but even if it were correct - what is the expected sum of numbers up to 10000000?

11. Jun 5, 2014

The user can click on the cross to finish it

12. Jun 5, 2014

Oh it's 2,147,483,647 and -2,147,483,647

Sum of natural numbers up to 10000000 is $5.0000005 \times 10^{13}$

13. Jun 5, 2014

### Staff: Mentor

And you still don't see where the problem is?

14. Jun 5, 2014