r+7(<=)12
r+7 should result: 0,1,2,3,4,5,6,7,8,9,10,11,12
so, here's the process:
r+7= 0
r= 0-7
r= -7
r+7= 1
r= 1-7
r= -6
r+7= 2
r= 2-7
r= -5
r+7= 3
r= 3-7
r= -4
r+7= 4
r= 4-7
r= -3
r+7= 5
r= 5-7
r= -2
r+7= 6
r=6-7
r= -1
r+7= 7
r= 7-7
r= 0
r+7= 8
r= 8-7
r= 1
r+7= 9
r= 9-7
r= 2
r+7= 10
r= 10-7
r= 3
r+7= 11
r= 11-7
r= 4
r+7= 12
r= 12-7
r= 5
r = { -7,-6,-5,-4,-3,-2,-1,0,1,2,3,4,5}
