n=1000000;
incircle=Compile[{},With[{pt={RandomReal[],RandomReal[]}},If[Norm[pt]<1,1,0]]];

4.0*Total[Table[incircle[],{n}]]/n

n=5000;
randpt=Compile[{},With[{pt={RandomReal[],RandomReal[]}},pt]];

Graphics[{If[Norm[#]<1,Red,Blue],Point[#]}&/@Table[randpt[],{n}]]