foo.c:15:15: warning: built-in function 'index' declared as non-function [enabled by default]
foo.c: In function 'cmp':
foo.c:18:2: error: unknown type name 'Data'
foo.c:18:11: error: 'Data' undeclared (first use in this function)
foo.c:18:11: note: each undeclared identifier is reported only once for each function it appears in
foo.c:18:17: error: expected expression before ')' token
foo.c:19:7: error: expected ';' before 'y'
foo.c:20:10: error: request for member 'num' in something not a structure or union
foo.c:20:15: error: 'y' undeclared (first use in this function)
foo.c:18:7: warning: variable 'x' set but not used [-Wunused-but-set-variable]
foo.c:21:1: warning: control reaches end of non-void function [-Wreturn-type]