/in/foo.c:1:1: warning: data definition has no type or storage class
    1 | n = int(input("请输入学校需要购买几种图书："))
      | ^
/in/foo.c:1:1: warning: type defaults to 'int' in declaration of 'n' [-Wimplicit-int]
/in/foo.c:1:5: error: expected expression before 'int'
    1 | n = int(input("请输入学校需要购买几种图书："))
      |     ^~~
/in/foo.c:10:40: error: stray '#' in program
   10 |         cost = price * quantity * 0.9  # 打9折
      |                                        ^
/in/foo.c:12:34: error: stray '#' in program
   12 |         cost = price * quantity  # 不打折
      |                                  ^