Output and Math Precision

[wey97]

Option Explicit
 
Private Sub Form_Load()
    Dim d As Double
    d = CDbl("999999999999999.01")
    d = d - CDbl("999999999999999")
    MsgBox d
    MsgBox 0.0000000001
    MsgBox CDbl("99999999999999999999999")
    MsgBox Sin(CDbl("99999999999999999999999"))
End Sub

Why does the first msgbox not output with any precision
when the second does?
Sin takes a double as an argument, so why does the last
statement give an error?

[wey97]

#include <iostream.h>
#include <math.h>

void main(void){
	double d;
	d = 999999999999999.01;
	d -= 999999999999999;
	cout << d << endl;
	cout <<  0.0000000001 << endl;
    cout << (double)99999999999999999999999;
    cout << sin(99999999999999999999999);
}

Won't compile.

[gdebacker]

From MSDN

Invalid procedure call or argument (Error 5)
Anargument probably exceeds the range of permitted values. For example, the Sin function can only accept values within a certain range. Positive arguments less than 2,147,483,648 are accepted, while 2,147,483,648 generates this error.

Greg

[wey97]

That explains it.
What about the loss of precision?

[gdebacker]

What about the loss of precision?

I have no idea, sorry.

Greg

[beachbum]

Originally posted by wey97
What about the loss of precision?

Sometimes u can work around the inprecision by reorganising the calculation. It would be difficult to do for a large number of complicated transactions.
eg

Private Sub Form_Load()
    Dim d As Double
    Dim e As Double
    Dim x As Integer
    Dim Mydouble As Double
    
    For x = 1 To 10
        Mydouble = Mydouble + 9 ^ x
        
        'This works exactly
        d = Mydouble + 1
        d = (d - Mydouble) / 10
        MsgBox d
    
        'while this doesnt
        d = Mydouble + 0.01
        d = d - Mydouble
        MsgBox d
    Next
End Sub

regards
Stuart