/in/foo.cc: In function 'int main()':
/in/foo.cc:11:11: warning: iteration 2001 invokes undefined behavior [-Waggressive-loop-optimizations]
    a[i][j]=false;
    ~~~~~~~^~~~~~
/in/foo.cc:10:13: note: within this loop
   for (j=0;j<=2001;j++)
            ~^~~~~~