#################################   
always @ (a or b )
begin
      case({a,b}) 
2'b00 : begin 
                sum = 1'b0; 
                carry = 1'b0;
                 end
2'b01 : begin 
                sum = 1'b1; 
                carry = 1'b0;
                 end
2'b10 : begin 
                sum = 1'b1; 
                carry = 1'b0;
                 end
2'b11 : begin 
                sum = 1'b0; 
                carry = 1'b1;
                 end
              

endcase 
end
##################################