Adding numbers from 1 to N in C#

问题

I'm writing code in C# and trying to add all of the numbers between the number 1 and N, N being the number that is inputted in a textbox. I'm doing this, at least trying to do this, by putting it into a while loop.

I have added all the numbers between 2 textboxes before but for some reason I'm driving myself crazy and can't figure this out. I'm a beginning programmer so please be gentle.

Any help would be greatly appreciated.

Edit: One of the six thousand things I've tried. I think this has me in an infinite loop?

       private void btnAddAll_Click(object sender, EventArgs e)
       {
           int n;
           int count = 0;
           int answer = 0;

           n = int.Parse(txtNum.Text);

           count = n;

           while (count >= 1)
           {
               answer = answer + count;
               count++;
           }
               lstShow.Items.Add("Sum = " + answer);
               lstShow.Text = answer.ToString();
       }

回答1:

Why not use Gauss formula. (N*(N+1))/2

private void btnAddAll_Click(object sender, EventArgs e)
{
     int n, answer;  
     n = int.Parse(txtNum.Text);
     answer = (n*(n+1))/2;
     lstShow.Items.Add("Sum = " + answer);
     lstShow.Text = answer.ToString();
}

回答2:

Your edit: you should decrement count.. Another edit, it appears I need to explain more: By decrement I mean --. The post or pre decrement operator decreases the value by 1.

If count keeps increasing by 1, count >=1 will never be met. You need to reduce count to 1.. hence count--;

Also I suggest you use TryParse(string,out int) ; or at least wrap the Parse call in a try catch block.

Here is a pointer in pseudocode:

GetInput From User
TryParse Input
If Between 1 and N
Declare sum = 1;

for i to N-1 
   sum+=i; 

/* if you don't want to use the for loop
  while i < N 
  sum+=i;
  inc i; */
Print sum

回答3:

If you change the ++ to a -- it should work as you want it to.

   int n;
   int count = 0;
   int answer = 0;

   n = 3;

   count = n;

   while (count >= 1)
   {
       answer = answer + count;
       count--; // here was the error
   }

   Console.WriteLine (answer);

Output: 6

Also, just for a point of additional interest you can use That uses Enumerable.Range and Enumerable.Sum instead of the while loop (probably goes beyond what is expected for a homework but it's useful to know what's out there).

answer =  Enumerable.Range(1, n).Sum();

回答4:

Debugging is an important skill for any programmer. There are some good tools in Visual Studio to help with debugging.

A good way to debug your code when you are stuck is to use 'breakpoints' and step through the code.

Select the line you want your code to stop at (e.g. n = int.Parse(txtNum.Text);) and press F9 - this will add a breakpoint at this line.

Now, when you run your programme, it will stop at the breakpoint. If you press F11, you can 'step' through the code one line at a time. You can hold your mouse over a variable to see its value while you are doing this.

You will quickly find the problem in your code if you do this.

来源：https://stackoverflow.com/questions/13060042/adding-numbers-from-1-to-n-in-c-sharp

标签

while-loop