/in/foo.c: In function 'main':
/in/foo.c:12:2: warning: implicit declaration of function 'Output' [-Wimplicit-function-declaration]
  Output(a, n);
  ^~~~~~
/in/foo.c:11:6: warning: unused variable 'i' [-Wunused-variable]
  int i, a[]={5,6,1,2,8,3,4,7}, n=8;
      ^
/tmp/cc6T57Ii.o: In function `main':
foo.c:(.text.startup+0x52): undefined reference to `Output'
collect2: error: ld returned 1 exit status