[THFS]

I am working on an algebra program that will do quadratic formulas for me, but for some reason I keep getting this error:

Run-time error '5':

Invalid procedure call or argument

This is my code:

b = Val(before_x.Text)
a = Val(before_x_power.Text)
c = Val(non_x.Text)
x_value_1 = -b + Sqr(b ^ 2 - 4 * a * c) / 2 * a
X1.Text = Str$(x_value_1)

All the name values are correct, so that's not the problem. When I click debug it highlights the line with the formula, so I think it's something to do with that. Anyone see a problem with it?

[AlbertB]

I am afraid I don't know VB, but I do know algebra. A suggestion! Have you rprogram detect a situation where:

( 4 * a * c ) > ( b ^ 2 )

This does happen with quadratics and will lead to a situation where you are trying to find the square root of a negative number, (easy for us if you know your complex numbers, but not for your computer).

Simply enclose your line of calculation in an "If - Then" statement to check for the condition and print an error message instead if it occurs.

[AlbertB]

Only a guess but I wonder if it does not like the way you have expressed your " -b " term. You could try ( -1 * b ) or even better rewrite it as:

x_value_1 = ( Sqr(b ^ 2 - 4 * a * c) - b ) / ( 2 * a )

[coderitr]

Step through the code in the debugger and try to determine which line the error occurs on. Then, if possible, simplify that line of code into two or more separate lines. This will make your code easier to follow for others that may come behind you.

[THFS]

I fixed the code, but now have another problem. Thanks for the If Then thing, that's helped with the negative squareroot thing, but now I want it to output text if it is impossible. I want it to say something like "Sorry, but this has no possible solution."
Here's the code now:

Private Sub first_x_value_Click()
a = Val(a.Text)
b = Val(b.Text)
c = Val(c.Text)
If (b ^ 2) > (4 * a * c) Then x_value_1 = (-b + Sqr(b ^ 2 - 4 * a * c)) / (2 * a)
If (b ^ 2) < (4 * a * c) Then x_value_1 = THIS IS WHERE I WANT THE TEXT
X1.Text = Str$(x_value_1)
End Sub

How would I get the text to be output into the textbox? I've tried a few things but keep getting errors. Once I get that done then the program will be complete.

[AbvAvgUser]

You can use msgbox functions. Or if you want it in a textbox, then textbox.text = "THIS IS WHERE I WANT THE TEXT"

[AlbertB]

Another observation if I may

Remember the formula for calculating the roots of a quadratic is actually:

(-b ( + or - ) ( sqr( b^2 - 4*a*c ) ) / (2*a)

The term ( b^2 - 4*a*c ) is called the discriminant and the + or - generally gives rise to two equally valid and differing solutions.

You have only considered adding the value of the discriminant. It may not be necessary to consider both cases in the case of your problem, but if you wanted it to cover all eventualities you should offer another branch to your program to include both.

[THFS]

Thanks, but I just haven't implemented that part yet. I don't know how to combine two formulas so I'm just going to do a separate one for the subtraction.

Thanks for the textbox help, it's working great now.

[AbvAvgUser]

good to know its working as you want it to