foo.c: In function 'main':
foo.c:19:9: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
    sum+=abs(num[i]-num[j]);
         ^~~
foo.c:28:2: warning: 'con' may be used uninitialized in this function [-Wmaybe-uninitialized]
  printf("%d\n",con);
  ^~~~~~~~~~~~~~~~~~

自豪的采用jd5进行评测(github.com/masnn/jd5)