程序代码：

&&求一元二次方程.prg
of = CREATEOBJECT("fm1")
of.Show 
READ EVENTS 

DEFINE CLASS fm1 as Form
    WindowType = 1
    ShowWindow = 2
    Desktop = .T.
    AutoCenter = .T.
    Caption="求一元二次方程"
    left=77
    top=29
    height=282
    width=852
    

    ADD OBJECT label1 as myLbl1 WITH top=39,left=203
    ADD OBJECT label2 as myLbl2 WITH top=46,left=239
    ADD OBJECT label3 as myLbl3 WITH top=39,left=346
    ADD OBJECT label4 as myLbl4 WITH top=39,left=346
    ADD OBJECT label5 as myLbl5 WITH top=42,left=252
    ADD OBJECT label6 as myLbl6 WITH top=46,left=483
    ADD OBJECT label7 as myLbl7 WITH top=40,left=551
    ADD OBJECT label8 as myLbl8 WITH top=196,left=48
    ADD OBJECT label9 as myLbl9 WITH top=24,left=24
    ADD OBJECT text1 as myTxt1 WITH top=52,left=143
    ADD OBJECT text2 as myTxt2 WITH top=52,left=287
    ADD OBJECT text3 as myTxt3 WITH top=52,left=419
    ADD OBJECT cmdCalc as myCmd1 WITH top=148,left=167
    ADD OBJECT cmdExit as myCmd2 WITH top=148,left=491
    ADD OBJECT cmdRetry as myCmd3 WITH top=244,left=683

    PROCEDURE UnLoad
        CLEAR EVENTS
    ENDPROC
ENDDEFINE

DEFINE CLASS myLbl1 as Label
    Visible = .T.
    caption = "x"
    BackStyle=0
    AutoSize=.T.
    FontSize=50
    
ENDDEFINE

DEFINE CLASS myLbl2 as Label
    Visible = .T.
    caption = "2"
    BackStyle=0
    AutoSize=.T.
    FontSize=20
    
ENDDEFINE

DEFINE CLASS myLbl3 as Label
    Visible = .T.
    caption = "x"
    BackStyle=0
    AutoSize=.T.
    FontSize=50
    
ENDDEFINE

DEFINE CLASS myLbl4 as Label
    Visible = .T.
    caption = "x"
    BackStyle=0
    AutoSize=.T.
    FontSize=50
    
ENDDEFINE

DEFINE CLASS myLbl5 as Label
    Visible = .T.
    caption = "+"
    BackStyle=0
    AutoSize=.T.
    FontSize=50
    
ENDDEFINE

DEFINE CLASS myLbl6 as Label
    Visible = .T.
    caption = "＝"
    BackStyle=0
    AutoSize=.T.
    FontSize=50
    
ENDDEFINE

DEFINE CLASS myLbl7 as Label
    Visible = .T.
    caption = "0"
    BackStyle=0
    AutoSize=.T.
    FontSize=50
    
ENDDEFINE

DEFINE CLASS myLbl8 as Label
    Visible = .T.
    caption = ""
    BackStyle=0
    AutoSize=.T.
    FontSize=20
    
ENDDEFINE

DEFINE CLASS myLbl9 as Label
    Visible = .T.
    caption = '说明：先输入方程的系数，然后按“求解”按钮，即可求出方程的根。'
    BackStyle=0
    AutoSize=.T.
    FontSize=12
    
ENDDEFINE

DEFINE CLASS myTxt1 as TextBox
    Visible = .T.
    caption = ""
    BackStyle=0
    BorderStyle=1
    AutoSize=.T.
    FontSize=40
    Height=49
    Width=61
    
ENDDEFINE

DEFINE CLASS myTxt2 as TextBox
    Visible = .T.
    caption = ""
    BackStyle=0
    BorderStyle=1
    AutoSize=.T.
    FontSize=40
    Height=49
    Width=61
    
ENDDEFINE

DEFINE CLASS myTxt3 as TextBox
    Visible = .T.
    caption = ""
    BackStyle=0
    BorderStyle=1
    AutoSize=.T.
    FontSize=40
    Height=49
    Width=61
    
ENDDEFINE

DEFINE CLASS myCmd1 as CommandButton
    Visible = .T.
    caption = "求解"
    height = 25
    width = 85
    
    PROCEDURE Click
        thisform.label8.caption=""  &&用label8输出方程的结果，先修改其caption属性为“”（空）。
        a=VAL(thisform.text1.value)  &&以下三行读取方程的系数
        b=VAL(thisform.text2.value)
        c=VAL(thisform.text3.value)
        IF a!=0
            d=b*b-4*a*c  &&求delta的值
            DO CASE
                CASE d=0
                    x=-b/(2*a)
                    thisform.label8.caption="方程有一个实根："+ALLT(STR(x,8,2))+"。"  &&把数值转换为字符时，要注意str()的用法，否则只有整数
                CASE d>0
                    x1=(-b+SQRT(d))/(2*a)
                    x2=(-b-SQRT(d))/(2*a)
                    thisform.label8.caption="方程有两个实根，分别是："+ALLT(STR(x1,8,2))+"和"+ALLT(STR(x2,8,2))+"。"
                CASE d<0
                    sb=-b(2*a)
                    xb=SQRT(-d)/(2*a)
                    thisform.label8.caption="方程有两个复数根，分别是："+ALLTRIM(STR(sb,8,2))+"＋"+"allt(STR(xb,8,2))+"i"+"和"+ALLTRIM(STR(sb,8,2))+"－"+ALLTRIM(STR(xb,8,2))+"i"+"。""
            ENDCASE
        ELSE
            IF b!=0
                thisform.label8.caption="方程是一次方程，其根为："+ALLTRIM(STR(-c/b,8,2))+"。"
            ELSE
                thisform.label8.caption="由于二次项和一次项的系统均为0，不能构成一个方程。"
            ENDIF
        ENDIF                      
    ENDPROC
ENDDEFINE

DEFINE CLASS myCmd2 as CommandButton
    Visible = .T.
    caption = "退出"
    height = 25
    width = 85
    
    PROCEDURE Click
        thisform.Release
    ENDPROC
ENDDEFINE

DEFINE CLASS myCmd3 as CommandButton
    Visible = .T.
    caption = "再来一题"
    height = 25
    width = 85
    
    PROCEDURE Click
        thisform.text1.value=""
        thisform.text2.value=""
        thisform.text3.value=""
        thisform.text1.setfocus
        thisform.refresh
    ENDPROC
ENDDEFINE