Loss from listed equity shares

Yes, you should show loss, this can help in set off against Any gain from these shares

Is it mandatory ?
if assessee don't want to show in his return can he avoid such loss?

It's better to disclose the loss incured from listed equity shares ( whether short term capital loss or long term capital loss ). You will only be benefitted in the future. This loss can be carried forward in the future and can be set off against any Capital Gain from Listed Equity Shares.

NOTE : Long Term Capital Loss can be set off only against Long Term Capital Gains. [ Section 70(3) ].