/in/foo.c: In function 'main':
/in/foo.c:3:6: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
      printf("enjoy yourself\n");
      ^~~~~~
/in/foo.c:3:6: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:3:6: note: include '<stdio.h>' or provide a declaration of 'printf'