/in/foo.c:2:1: warning: data definition has no type or storage class
    2 | a=int(input("请输入边长（单位厘米）："))
      | ^
/in/foo.c:2:1: warning: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
/in/foo.c:2:3: error: expected expression before 'int'
    2 | a=int(input("请输入边长（单位厘米）："))
      |   ^~~