VHDL二输入与非门

二输入与非：检测显示错误 10500 VHDLsyntax error at and2.vhd(8) near text”;”;expecting”is”要怎么改呀

Judging from the error message, it looks like you have a syntax error in your VHDL code for the 2-input NAND gate. The message says it is expecting an "is" keyword but found a ";" instead.
To fix this, the structure of a basic VHDL entity-architecture block should be:

vhdl
entity <entity_name> is
   port (
      <port_list> 
   );
end entity;

architecture <arch_name> of <entity_name> is
begin
   <logic>
end architecture; 

So for a 2-input NAND gate, the code should be:

```bash
vhdl
entity nand_gate is
   port (
      a, b: in std_logic;
      q: out std_logic
   );   
end entity;

architecture structural of nand_gate is 
begin
   q <= a nand b;  
end architecture;

```
Some key points:

1. The entity declaration starts with "entity" and ends with "end entity;".
2. The architecture body starts with "architecture" and ends with "end architecture;".
3. The "is" keyword must be used after both "entity" and "architecture" declarations.
4. Use "port" to define the input/output ports within the entity.
5. The signal assignments and logic is defined between "begin" and "end architecture;".
   So in summary, to fix your syntax error, make sure to use "is" after "entity" and "architecture", define the ports correctly in the entity, and place the logic between "begin" and "end architecture;".
   Let me know if you have any other questions! I'd be happy to help explain VHDL syntax and constructs.