types

see how variable was declared as (int, string, etc…):

declare -p MYVAR

declare a variable as an integer only (only integers can be stored inside the variable):

declare -i NEWVAR=10
# doing something like this will assign 0 to the variable: NEWVAR="Testing"
# removing the integer only lock on a variable: declare +i NEWVAR

declare a variable as read-only:

declare -r NEWVAR="Testing"
# can also be declared this way: readonly NEWVAR="Testing"