If-Then statements and validating events in VB.net

[GeogImag]

This is my first post.....


I have created a solution that is one form. It is a project designed to calculate the area of a cube. I have the calculations correct but need to validate the entries that are in my text boxes (width, height, and length). Only entries that have positive numbers (numbers > 0) will be allowed. If the txt entry is incorrect when the user leaves that particular text box, the text entry should turn red. If the user attempts to calculate the cube area, then an error window should pop up when the calculate_click event occurs. I know I am supposed to use If then statements in the validate event but am unsure of how to do it. Can anyone help????

I know it will be good to include the code and I have done so in a text file. If I can post the whole project folder (.sln, .vb, .vbproj files, etc) and that is better then I will. Hopefully this text file will suffice.

Thanks ahead of time and I look foward to suggestions