/in/foo.c: In function 'main':
/in/foo.c:21:1: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
 scanf( "%d" ,&n);
 ^~~~~
/in/foo.c:21:1: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:21:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:31:1: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
 printf("%d ",a[i]);
 ^~~~~~
/in/foo.c:31:1: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:31:1: note: include '<stdio.h>' or provide a declaration of 'printf'