/in/foo.c: In function 'main':
/in/foo.c:5:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d",&n);
  ^~~~~
/in/foo.c:5:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:5:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:23:8: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
   sum+=abs(a[x-1]-a[i]);
        ^~~
/in/foo.c:24:2: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
  printf("%d\n",sum);
  ^~~~~~
/in/foo.c:24:2: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:24:2: note: include '<stdio.h>' or provide a declaration of 'printf'