> echo "mystr" # no split

You probably meant to include $

echo "$mystr" # no split

Still, echo is not good for these examples as for it the split doesn't matter and can't be detected, whereas for other commands (or even calls of functions) it indeed can matter.

This example, I think, illustrates the differences between quoted and unquoted use of $name (as present in the current shells) better (to those who aren't familiar with the nuances of shells):

    f() {
        echo "param 1: |$1|"
        echo "param 2: |$2|"
        echo "param 3: |$3|"
    }

    x=
    y="55 66"
    f "$x" "$y"
    echo
    f $x $y

    #Output is:
    #param 1: ||
    #param 2: |55 66|
    #param 3: ||
    #
    #param 1: |55|
    #param 2: |66|
    #param 3: ||

BTW, the fact that shell splits and echo joins is VERY confusing to a beginner. For example:

mystr='a b c' # two spaces between each

    $ echo $mystr
    a b c   # why is there only one space?

    char line[100];  // truncates lines longer than 100 chars