View Compilation Error

0_0_38348618_941.cpp: In function 'int main()':
0_0_38348618_941.cpp:2:17: error: 'a' was not declared in this scope
 #define ST sort(a,a+n,cmp);
                 ^
0_0_38348618_941.cpp:19:3: note: in expansion of macro 'ST'
   ST(s,s+n,cmp);
   ^