Where is the problem in this program? It goes to an infinite loop when I tried to run this program

SystemVerilog
, ,
1 
class subhra;
  rand bit[3:0] a;
   int q[$];
 constraint b{a<15;}
endclass

module test;
    subhra su =new();
initial begin

    while (su.q.size<16) begin
     for(int i=0;i<16;i++) begin
        su.randomize();
      su.q.push_back(su.a);
      su.q=su.q.unique();
      end
    end
    su.q.shuffle;
  $display("q:%p",su.q);
end
endmodule
2

In reply to Subhra Bera:
Because there are only 15 integer values less than 15, and your q needs to have 16 or more values to get out of the while loop.