用c#从键盘上输入一个整数,然后计算1+2+……n的值

 public partial class Form1 : Form
    {
        string key = null;
        public Form1()
        {
            InitializeComponent();
            this.KeyPreview = true;
        }

        private void Form1_KeyPress(object sender, KeyPressEventArgs e)
        {
            int num = 0;
            if (int.TryParse(e.KeyChar.ToString(), out num))
            {
                key += num.ToString();
                Text = key;
            }
        }
        private void Form1_KeyDown(object sender, KeyEventArgs e)
        {
            object a = sender;
            if (e.KeyValue.ToString().Equals("13"))
            {
                if (key != null)
                {
                    int num = 0;
                    int sum = 0;
                    if (int.TryParse(key, out num))
                    {
                        for (int i = 1; i <= num; i++) {
                            sum += i;
                        }
                    }
                    Console.WriteLine(sum);
                    key = null;
                }
            }
        }
    }

winform中让窗体得到焦点，会一直接收你输入的数字，直到按下{Enter}键，自动算 1-n的值，如果是控制台那些，自己修改一下也能达到同样的效果。

Console.WriteLine("请输入一个整数：");
            try
            {
                int n = Convert.ToInt32(Console.ReadLine());
                int sum = 0;
                while (n > 0)
                {
                    sum += n;
                    n--;
                }
                Console.Write(sum);
            }
            catch
            {
                Console.WriteLine("您输入的不是数字");
            }
            Console.ReadKey();

输入后(假设为控制台)

int sum=0;
int n=Console.ReadLine();
for(int i=1;i<=n;i++){
    sum+=i;
}
Console.WriteLine(sum);