Mux3to1.v

module Mux3to1( data0_i, data1_i, data2_i, select_i, data_o );

parameter size = 0;			   
			
//I/O ports               
input wire	[size-1:0] data0_i;          
input wire	[size-1:0] data1_i;
input wire	[size-1:0] data2_i;
input wire	[2-1:0] select_i;
output wire	[size-1:0] data_o; 

//Main function
/*your code here*/

assign data_o = (!select_i)?data0_i: (select_i==2'd1)?data1_i: (select_i==2'd2)?data2_i: 
				0;//default: assign size'd0 to output

endmodule