/in/foo.c: In function 'main':
/in/foo.c:15:12: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
    out=out+abs(a[j]-a[i]);
            ^~~
/in/foo.c:23:2: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
  printf("%d\n",res);
  ^~~~~~~~~~~~~~~~~~