In these situations with an overwhelming material advantage against an opponent whose only moving piece is the king, be really careful anytime your move does not check the king. Here is an alternative on move 36 that would have mated. (30...Rfe8# also could have been played.)
Others have politely explained the rule which you were unaware of. There are 2 types of response to the explanations you could have chosen:
1. 'It's a stupid rule, it's ridiculous that it doesn't count as a win for me.'
2. 'Thanks for the answers guys, now it's been explained to me I'll be sure to avoid letting it happen again.'
You have chosen poorly, just as you did when advancing the c pawn instead of giving checkmate with the rook.