While vs Until

Good comparison
Example 1
Example 2

Now only use "sum" function
Example 3

Step function to par numbers
Example 4

Step to sum
For In, Each
Example 1
Example 2
Altering loop control
Using Next to prevent error
Using Redo to prevent error
Using break to prevent error. Not recommended.
Exercises with While loop, if/elsif/else
Exercises with for in, when, case