+= operator with if statement gives errors

[freeflow]

I'd appreciate a pointer as to why I'm getting two errors for this line of code 
one for the + in += One for 'if myMoves == UP: 1 else: -1'
    
    
    myFloor += if myMoves == UP: 1 else: -1
    
    
    
    Run

myfloor is defined as int, myMoves is derived from 'for myMoves in s.data' 
where s.data is a string and UP is '('