Update sort_demo.cpp
Update sort_demo.cpp

added the head file for built-in function rand()
qvex/algorithms,switchkiller/algorithms,xtaci/algorithms,tempbottle/algorithms,hengwusanren/algorithms,xmfbit/algorithms,xtaci/algorithms,greyg00s/algorithms,zhenglaizhang/algorithms,hengwusanren/algorithms,jacklicn/algorithms,qvex/algorithms,lanbing510/Algorithms,dumubuchenglin/algorithms,sigma-random/algorithms,ashwini0529/algorithms-1,NoSmartNoMan/algorithms,noname007/algorithms,dumubuchenglin/algorithms,shijiaxing/algorithms,shijiaxing/algorithms,jacklicn/algorithms,xmfbit/algorithms,greyg00s/algorithms,noname007/algorithms,ashwini0529/algorithms-1,sigma-random/algorithms,fengzhyuan/algorithms,allengaller/algorithms,tempbottle/algorithms,switchkiller/algorithms,fengzhyuan/algorithms,lanbing510/Algorithms,M4573R/algorithms-1,allengaller/algorithms,zhenglaizhang/algorithms,fw1121/algorithms,fw1121/algorithms,NoSmartNoMan/algorithms,M4573R/algorithms-1