我在10月份發表過一篇隨筆“畫函數圖形的C#程序，兼論一個病態函數”，在那篇隨筆中寫道：
這個畫函數圖形的C#程序有一個嚴重的缺點，就是函數表達式是直接寫的源程序中的，不能象SciLab和Matlab那樣交互式地輸入。 后來，根據“空間/IV”的評論，我寫了個動態生成用戶輸入的函數表達式的類，用以改進這個畫函數圖形的C#程序。下面是該程序的運行效果：


可以看到，不但要畫的函數的表達式可以由用戶動態地輸入，而且函數自變量的范圍也可以是常量表達式。 下面就是源程序：
//?plot.cs:?畫函數圖形,?編譯方法:?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;?//?屏幕保留區域的高度

????TextBox?tbxX0,?tbxX1;??//?函數自變量的取值范圍
????TextBox?tbxExpression;?//?函數的表達式
????
????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);
????}

????//?點擊“刷新”按鈕時重繪程序主窗口
????void?BtnSubmit_Click(object?sender,?EventArgs?e)
????{
??????Invalidate();
????}
????
????/**//*
????//?因為本程序使用?C#?的反射功能動態生成數學表達式并計算其值
????//?所以重畫時有點慢，如果你的計算機的速度不是非常快的，
????//?就不要在窗口改變大小時強制重繪，而是通過點擊發“刷新”按鈕重繪。
????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);?//?畫圖區和保留區的分界線
????????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);??//?函數自變量每單位值用多少個象素表示
????????Out(gc,?5,?"ry:{0}",?1?/?ry);??//?函數的值每單位值用多少個象素表示
????????Out(gc,?6,?"r?:{0}",?rx?/?ry);?//?該值如果小于1表示圖形縱向被壓扁，反之則被拉伸
????????pen.Color?=?Color.Green;
????????int?j?=?j1?+?(int)(y0?/?ry);
????????if?(j?>=?j0?&&?j?<=?j1)?gc.DrawLine(pen,?i0,?j,?i1,?j);?//?x坐標軸
????????int?i?=?i0?-?(int)(x0?/?rx);
????????if?(i?>=?i0?&&?i?<=?i1)?gc.DrawLine(pen,?i,?j0,?i,?j1);?//?y坐標軸
????????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);?//?畫函數的圖形
????????}
??????}
??????catch?(Exception?ex)
??????{
????????Out(gc,?0,?ex.Message);
??????}
??????base.OnPaint(e);
????}
????
????//?函數值的取值范圍
????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;
??????}
????}
????
????//?在指定的位置寫字符串
????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());
????}
??}
}

轉載于:https://www.cnblogs.com/gjahead/archive/2007/08/18/861164.html

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