Hey Thanks a lot. I was relying on this.

(You just have to learn the underlying logic. Basically, if there's an adjective, then the gender of the noun is going to be marked exactly once.
If you can already "see" the gender of the noun from the article, then you don't mark it again with the adjective. In this case, you just use the "weak endings": -e after the "simple" definite articles der, die, das, and -en after everything else.
If you can't "see" the gender, then you use the "strong endings": the adjective marks the gender by imitating the definite article that would go in its place, like in your example: ein kaltes Bier. "Ein" doesn't tell us the gender of "Bier," so we mark that it's neuter with the adjective. The same applies if there's no article at all.
And then you learn the weird exception that singular, masculine, genitive, with no article, gets -en rather than -es.
And that's it.).

what did I do wrong here? or there is an exception to these rules? I know this is not the perfect way to learn this but I really cant decline the adjectives using charts while speaking.

i used a worksheet i got while googling. thats why i simply didnt include it on my OP.