In C string literals can be compared with equality operator (==), but what the user enters and you store in BATTLE_INPUT is not a string literal.
When you compare the BATTLE_INPUT to "Attack" what you really compare is the memory address stored in your variable and the memory address of the string literal. You can see this is unlikely to match.
To compare strings, use the strcmp() function from the "string.h" library.
Your code should look like this
if (strcmp(BATTLE_INPUT, "Attack") == 0)
Good luck!