带有循环的C#乘法表程序一直处于冻结状态，两个事件不起作用

我一直在C#/Visual Studio中开发这个简单的乘法表程序，它一直给我带来麻烦，因为循环（尤其是do-while）对我来说非常困难。我应该使用嵌套的for循环和嵌套的do-whil循环，尽管我没有得到任何错误，但当我调试或运行程序并单击while loop按钮时，它冻结了，需要停止；forloop按钮仅在单击时显示"0"，但dowhile循环按钮似乎工作正常。

我相信这些是有问题的部分-对于循环：

  for (r = 1; r < 10; r++)
        {
            for (c = 1; c < 10; c++)
            {
                intResult = r * c;
                if (intResult < 10)
                    strSpace = "  ";  //two spaces 
                else
                    strSpace = " ";   //one space
                txtTable.AppendText(strSpace); // insert space
                txtTable.AppendText(intResult.ToString());  //insert result
                txtTable.AppendText("'r'n");  //Move down one line
            }
        }
    }

While loop:

  private void btnWhileLoop_Click(object sender, EventArgs e)
    {
        int r = 0; //row
        int c = 0; //column
        int intResult;
        string strSpace;
        txtTable.Clear();    //clear the text box
        txtTable.Refresh();  //refresh the form before exiting the method
        Thread.Sleep(1000);  //wait one second to see the clear text box
        //Outer loop goes down the rows
         r = 1; //initialize r
        do
        {
           //Inner loop goes across the columns
            c = 1; //initialize c
            do
            {

               intResult = r * c;
            } while (r < 10);
           } while (c < 10);
                strSpace = "  ";
                txtTable.AppendText(strSpace); // insert space
               txtTable.AppendText(intResult.ToString());  //insert result
                c++;  //increment c
        {
            txtTable.AppendText("'r'n");  //Move down one line
            r++;  //increment r
        }
    }

完整参考代码：

    namespace CS10b
{
    public partial class frmCS10b : Form
    {
        public frmCS10b()
        {
            InitializeComponent();
        }

        private void btnWhileLoop_Click(object sender, EventArgs e)
        {
            int r = 0; //row
            int c = 0; //column
            int intResult;
            string strSpace;
            txtTable.Clear();    //clear the text box
            txtTable.Refresh();  //refresh the form before exiting the method
            Thread.Sleep(1000);  //wait one second to see the clear text box
            //Outer loop goes down the rows
             r = 1; //initialize r
            do
            {
               //Inner loop goes across the columns
                c = 1; //initialize c
                do
                {

                   intResult = r * c;
                } while (r < 10);
               } while (c < 10);
                    strSpace = "  ";
                    txtTable.AppendText(strSpace); // insert space
                   txtTable.AppendText(intResult.ToString());  //insert result
                    c++;  //increment c
            {
                txtTable.AppendText("'r'n");  //Move down one line
                r++;  //increment r
            }
        }

        //Modify the nested while loops used above to nested do-while loops
        private void btnDoWhileLoop_Click(object sender, EventArgs e)
        {
            int r = 0; //row
            int c = 0; //column
            int intResult;
            string strSpace;
            txtTable.Clear();    //clear the text box
            txtTable.Refresh();  //refresh the form before exiting the method
            Thread.Sleep(1000);  //wait one second to see the clear text box
            txtTable.AppendText("'r'n");
            //Outer loop goes down the rows
            //initialize r
            //do
            //Inner loop goes across the columns
            //initialize c
            //do
            for (r = 1; r < 10; r++)
            {
                for (c = 1; c < 10; c++)
                {
                    intResult = r * c;
                    if (intResult < 10)
                        strSpace = "  ";  //two spaces 
                    else
                        strSpace = " ";   //one space
                    txtTable.AppendText(strSpace); // insert space
                    txtTable.AppendText(intResult.ToString());  //insert result
                    txtTable.AppendText("'r'n");  //Move down one line
                }
            }
        }

        //Modify the nested while loops used above to nested for loops
        private void btnForLoop_Click(object sender, EventArgs e)
        {
            int r = 0; //row
            int c = 0; //column
            int intResult;
            string strSpace;
            txtTable.Clear();    //clear the text box
            txtTable.Refresh();  //refresh the form before exiting the method
            Thread.Sleep(1000);  //wait one second to see the clear text box
            txtTable.AppendText("'r'n"); 

            //Outer loop goes down the rows

            //for (initialize r; Boolean Condition, increment r)
             {
                //Inner loop goes across the columns
                //for (initialize c; Boolean Condition, increment c)
                {
                    intResult = r * c;
                    if (intResult < 10)
                        strSpace = "  ";  //two spaces 
                    else
                        strSpace = " ";   //one space
                    txtTable.AppendText(strSpace); // insert space
                    txtTable.AppendText(intResult.ToString());  //insert result
                }
                txtTable.AppendText("'r'n");  //Move down one line
            }
        }

        private void btnExit_Click(object sender, EventArgs e)
        {
            this.Close();
        }

}
}//end of form
//end of namespace

谢谢。