/in/foo.c: In function 'main':
/in/foo.c:11:2: warning: implicit declaration of function 'system' [-Wimplicit-function-declaration]
  system("pause");
  ^~~~~~
/in/foo.c: In function 'output':
/in/foo.c:23:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^