面是该程序的运行效果： 
可以看到，此程序不但要画的函数的表达式可以由用户动态地输入，而且函数自变量的范围也可以是常量表达式。 下面就是源程序：
// plot.cs: 画函数图形, 编译方法: csc /t:winexe plot.cs Expression.cs using System; using System.Drawing; using System.Windows.Forms; using Skyiv.Util; namespace Skyiv.Ben.Plot {
sealed class PlotForm : Form
{
const int yBase = 24; // 屏幕保留区域的高度
TextBox tbxX0, tbxX1; // 函数自变量的取值范围
TextBox tbxExpression; // 函数的表达式
PlotForm()
{
SuspendLayout();
Button btnSubmit = new Button();
btnSubmit.Text = "刷新";
btnSubmit.Location = new Point(0, 0);
btnSubmit.Size = new Size(48, 24);
btnSubmit.Click += new EventHandler(BtnSubmit_Click);
tbxX0 = new TextBox();
tbxX0.Text = "-Math.PI";
tbxX0.Location = new Point(55, 3);
tbxX0.Size = new Size(100, 20);
tbxX1 = new TextBox();
tbxX1.Text = "Math.PI";
tbxX1.Location = new Point(160, 3);
tbxX1.Size = new Size(100, 20);
tbxExpression = new TextBox();
tbxExpression.Text = "Math.Sin(x)";
tbxExpression.Location = new Point(265, 3);
tbxExpression.Size = new Size(335, 20);
tbxExpression.Anchor = (AnchorStyles.Top | AnchorStyles.Left | AnchorStyles.Right);
Controls.AddRange(new Control[]{btnSubmit, tbxX0, tbxX1, tbxExpression});
Text = "Plot";
BackColor = Color.White;
ClientSize = new Size(600, 600 + yBase);
// WindowState = FormWindowState.Maximized;
ResumeLayout(false);
}
// 点击“刷新”按钮时重绘程序主窗口
void BtnSubmit_Click(object sender, EventArgs e)
{
Invalidate();
}
/*
// 因为本程序使用 C# 的反射功能动态生成数学表达式并计算其值
// 所以重画时有点慢，如果你的计算机的速度不是非常快的，
// 就不要在窗口改变大小时强制重绘，而是通过点击发“刷新”按钮重绘。
protected override void OnSizeChanged(EventArgs e)
{
Invalidate();
base.OnSizeChanged(e);
}
*/
protected override void OnPaint(PaintEventArgs e)
{
Graphics gc = e.Graphics;
try
{
double x0 = new Expression(tbxX0.Text).Compute(0);
double x1 = new Expression(tbxX1.Text).Compute(0);
Size size = ClientSize;
int i0 = 0;
int i1 = size.Width - 1;
int j0 = yBase;
int j1 = size.Height - 1;
Pen pen = new Pen(Color.Black, 1);
gc.DrawLine(pen, i0, j0, i1, j0); // 画图区和保留区的分界线
double rx = (x1 - x0) / (i1 - i0);
double y0, y1;
Expression fx = new Expression(tbxExpression.Text);
GetFunctionValueRange(fx, x0, rx, i0, i1, out y0, out y1);
double ry = (y1 - y0) / (j1 - j0);
Out(gc, 0, "ClientSize: {0}x{1}", i1 - i0 + 1, j1 - j0 + 1);
Out(gc, 1, "f(x): " + tbxExpression.Text);
Out(gc, 2, "x:[{0}, {1}] range:{2}", x0, x1, x1 - x0);
Out(gc, 3, "y:[{0}, {1}] range:{2}", y0, y1, y1 - y0);
Out(gc, 4, "rx:{0}", 1 / rx); // 函数自变量每单位值用多少个象素表示
Out(gc, 5, "ry:{0}", 1 / ry); // 函数的值每单位值用多少个象素表示
Out(gc, 6, "r :{0}", rx / ry); // 该值如果小于1表示图形纵向被压扁，反之则被拉伸
pen.Color = Color.Green;
int j = j1 + (int)(y0 / ry);
if (j >= j0 && j <= j1) gc.DrawLine(pen, i0, j, i1, j); // x坐标轴
int i = i0 - (int)(x0 / rx);
if (i >= i0 && i <= i1) gc.DrawLine(pen, i, j0, i, j1); // y坐标轴
pen.Color = Color.Red;
for (i = i0; i <= i1; i++)
{
double x = x0 + (i - i0) * rx;
double y = fx.Compute(x);
if (double.IsInfinity(y) || double.IsNaN(y)) continue;
j = j1 - (int)((y - y0) / ry);
if (j > j1 || j < j0) continue;
gc.DrawLine(pen, i, j, i + 1, j); // 画函数的图形
}
}
catch (Exception ex)
{
Out(gc, 0, ex.Message);
}
base.OnPaint(e);
}
// 函数值的取值范围
void GetFunctionValueRange(Expression fx, double x0, double rx, int i0, int i1, out double y0, out double y1)
{
y0 = double.MaxValue;
y1 = double.MinValue;
for (int i = i0; i <= i1; i++)
{
double x = x0 + (i - i0) * rx;
double y = fx.Compute(x);
if (double.IsInfinity(y) || double.IsNaN(y)) continue;
if (y0 > y) y0 = y;
if (y1 < y) y1 = y;
}
}
// 在指定的位置写字符串
void Out(Graphics gc, int line, string fmt, params object [] args)
{
gc.DrawString(string.Format(fmt, args), new Font("Courier New", 10), Brushes.Blue, new PointF(5, yBase + 15 * line));
}
static void Main()
{
Application.Run(new PlotForm());
}
}
}
原文：http://skyivben.cnblogs.com/archive/2005/11/01/266649.html