/in/foo.c: In function 'sort':
/in/foo.c:5:3: warning: implicit declaration of function 'sink' [-Wimplicit-function-declaration]
   sink(arr,i,length-1);
   ^~~~
/in/foo.c: In function 'sink':
/in/foo.c:29:3: warning: implicit declaration of function 'swap' [-Wimplicit-function-declaration]
   swap(arr,k,j);
   ^~~~
/in/foo.c: In function 'push':
/in/foo.c:20:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^