You can only assign an integer number (i.e. a number without decimal part) to an integer data type.
"integer" is a string, so it's not a number (and thus not an integer)
90.1 has a decimal part, so it's not an integer
'1' is a string, so it's not a number (and thus not an integer)
true is a boolean, so it's not a number (and thus not an integer)
-25
0
423190
0.1 has a decimal part, so it's not an integer
