/in/foo.c: In function 'main':
/in/foo.c:13:16: warning: iteration 2 invokes undefined behavior [-Waggressive-loop-optimizations]
    b[j][i]=a[i][j];}
            ~~~~^~~
/in/foo.c:11:5: note: within this loop
     for(i=0;i<3;i++)
     ^~~