Use of wire inside an always block?

问题:

Can I use a wire inside an always block? Like for example:

        wire [3:0]a;
        assign a=3;

        always @(c)
           begin
                d=a+c;
           end

It got compiled without throwing any error. Why?

回答1:

Yes, you can use a wire's value inside an always block, you just can not assign a value to a wire in always or initial block.

The only real difference between a wire and reg is the syntax for assigning values.

In the above example d could also have been created as a wire, these are equivalent:

reg [3:0] answer_reg;
always @* begin
  answer_reg = a + c;
end

wire [3:0] answer_wire;
assign answer_wire = a + c;