Perform the test and exit on false

The first thing that happens following entry is that a condition is tested for true or false.

If the test returns false, control simply exits the loop structure without taking any action at all.

Perform some actions and repeat the test on true

If the test returns true:

• One or more actions are performed in sequence.
• The condition is tested again.

During each iteration, if the test returns false, control exits the structure.  If the test returns true, the entire cycle is repeated.