Braces should not be used in if the if statement is inside a flutter widget
if (int.parse(m_id) > int.parse(cm_id) || int.parse(d_id) > 4)
      Container(
         width: 0.23 * size,
         height: 0.23 * size,
         child: Image.asset('assets/images/days/day4k.png'),
   ),
The above should work just fine
If you do happen do have an if else statement, you still won't employ the use of braces, just remove the , at the end of the of the first widget
if (int.parse(m_id) > int.parse(cm_id) || int.parse(d_id) > 4)
    Container(
       width: 0.23 * size,
       height: 0.23 * size,
       child: Image.asset('assets/images/days/day4k.png'),
    ) //no comma here
else
    Container(), //comma here
Also, If you have an else if statement, you would also approach it in the same way
if (int.parse(m_id) > int.parse(cm_id) || int.parse(d_id) > 4)
    Container(
       width: 0.23 * size,
       height: 0.23 * size,
       child: Image.asset('assets/images/days/day4k.png'),
    ) //no comma here
else if (condition here)
    Container() //no comma here
else
    Container(), //comma here
     
    
elsestatement, use anotherifor move the code into a function returning a widget.