foo.c: In function 'distance':
foo.c:22:12: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
    s = s + abs(a[i] - a[x]);
            ^~~
foo.c:19:6: warning: unused variable 'i' [-Wunused-variable]
  int i, s = 0;
      ^

自豪的采用jd5进行评测(github.com/masnn/jd5)