This is just a confirmation. Are barcodes symmetric. By symmetric I mean, if I rotate the barcode by 180 degrees. Will it have the same data decoded. Basically does angle matter while scanning barcode? And are there any exceptions in the type of barcode.
No, the barcodes themselves are generally not symmetrical (I'll clarify that - you may be able to find one that is symmetrical but the vast majority of the standard ones are not).
However, any decent reader (such as the ones at your local supermarket) will scan in a large number of different directions to take care of this, not just backwards and forwards but at other angles as well. So you can generally rotate them to your heart's content.
Even the ones that scan in a line (such as some hand-held units) may scan both directions - it depends on what you've paid for. Of course, if you have a "Dodgy Brothers" brand reader, you'll probably find it won't do that.
Some barcode standards will allow for detecting upside down barcodes. For example UPCA swaps black and white on the right hand side so that readers can adjust for it.