[![jjg](https://i.stack.imgur.com/my7IU.png)](https://i.stack.imgur.com/my7IU.png)

why at C . the shear force V change from -0.5 to 0.5 ? We wantg to determine the shear force at different location , and a unit force is applied at arbitary location ( measured from A) ... 

IMO , there's no upwards force of 1 acting exactly on C , so the shear force will decrease from -0.5 at C to the cantilever end .