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Hi
I wanna write this but the answer is wrong ...
http://up.upinja.com/zvhev.png
I don't know which part i have coded wrong ...
Thnx

C#
```Console.WriteLine("Enter two Numbers to start the Equation (X=Number , N=Power)" + "");
double sum = 0;
double up = 1;
int down = 1;
double sentence;
for (int i = 1; i < N; i++)
{
up = Math.Pow(X, N);
down = N * i;
sentence = up / down;
sum += sentence;
}
Console.WriteLine("The Sum is : " + sum);```

What I have tried:

changing all the assignments ...
Posted
Updated 8-Nov-18 5:06am
v2
Richard MacCutchan 8-Nov-18 11:35am
The problem is most likely due to the maths involved (which is impossible to guess) rather than the code.
jsc42 8-Nov-18 16:56pm
The PNG has a formula like

sum = x + (x^2)/2! + (x^3)/3! + . . . + (x^N)/N!
(where I am using ^ as the exponentiation operator)

You need to understand the ! (factorial) operator and the fact that this is an infinite sequence (the N represents a sufficiently large number). Any reasonable Computer Science text book will tell you how to handle infinite sequences. Hint: Do not blithely get the terms and add them; you will need to think about the pattern between the adjacent terms. If you think about what the parts in the terms are doing, you will see why.

## Solution 2

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:
```Input   Expected output    Actual output
1            2                 1
2            4                 4
3            6                 9
4            8                16```
Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:
C#
```private int Double(int value)
{
return value * value;
}```

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

## Solution 1

Run it under the debugger (that's what we'd have to do). You'll probably find your problem.

BTW, just saying "the answer is wrong" is NOT enough for us to help you, because we don't know your sample input or the expected output, much less what you're even trying to do.