fix: declare reg inside module header

Author: pineylilly

ex04_4_input_multiplexer/mux_4.v

@@ -1,11 +1,9 @@
 module mux_4 (
     input a, b, c, d,
     input [1:0] sel,
-    output out
+    output reg out
 );
 
-    reg out;
-
     always @(*) begin
         case(sel)
             2'b00: out = a;

ex04_4_input_multiplexer/mux_4_ifelse.v

@@ -1,11 +1,9 @@
 module mux_4_ifelse (
     input a, b, c, d,
     input [1:0] sel,
-    output out
+    output reg out
 );
 
-    reg out;
-
     always @(*) begin
         if (sel == 2'b00) begin
             out = a;