showing a form based on value of a string containing the form's name

Hello
I have a string like str1 that contain the name of a form like Form33. In fact the str1 determines which form should be loaded and shown. The form may change with its number. How can I show the form through converting the string to a form?

Thank you very much for your help.

str1="Form33"

convert str1 to object obj as Form

obj.show