Вычисление площади треугольника по его трем сторонам (Формула Герона)

Public s As Double
Public Sub pltr(a As Double, b As Double, с As Double, pi As Double) 
pp = (a + b + c) / 2 
pp = pp* (pp - a) * (pp - b) * (pp - c)
 If pp < 0 Then
MsgBox "He верно заданы параметры", 16, "Ошибка" 
Else
pl = pp ^ 0.5 
End If 
End Sub
 
Private Sub Checkl_ Click()
If Check1.Value Then 
Label4.Capiion = Str(Round(s)) 
Else
Label4. Caption = Str(s) 
End If 
End Sub
 
Private Sub Command1_Click()
Dim x As Double, у As Double, z As Double
x = Val(Text1)
y= Val(Text2)
z=Val(Text3)
Call pltr(x, y, z, s)
pltr x, y, z, s
If Check1.Value Then
Label4.Caption = Str(Round(s))
Else
Label4.Caption = Str(s) 
End If 
End Sub
Private Sub Form_Load() 
Textl =0
Text2 = 0 
Text3 =0
Label4.Caption = "Результат" 
End Sub

Private Sub cmdStart_Click()
A = Val(textA.text)
B = val(textB.text)
C = val(textC.text)
P = A + B + C
Pp = P / 2
S = Sqr(Pp * (Pp - A) * (pp  - B)  * (Pp - C))
txtP.text = Str(p)
txtS.text = Str(s)
End sib