1. Do/Loops A loop repeats a series of instructions. An iteration is a single execution of the statement(s) in the loop. Used when the exact number of iterations is unknown A Do/Loop terminates based on a specified condition. Execution of the loop continues while a condition is True or until a condition is True. The condition can be placed at the top or the bottom of the loop.

2. The Do and Loop Statements — General Form Do {While |Until} condition ' Statements in loop. Loop --OR-- Do ' Statements in loop. Loop {While | Until} condition Top of Loop Condition, Pretest/Entry test Bottom of Loop Condition, Posttest/ Exit

3. Pretest vs. Posttest Pretest — loop may never be executed since tested BEFORE running. Do While … Loop Do Until … Loop Posttest — loop will always be executed at least once. Do … Loop While Do … Loop Until

4. Pretest vs. Posttest Diagram

5. The Boolean Data Type Revisited Can help when searching a list for a specific value Boolean variable is always in one of two states: True or False. When a particular situation occurs, set Boolean variable to True. Use a loop to check for True Many programmers refer to Boolean variables as switches or flags. Switches have two states — on or off. Flags are considered either up or down.

6. For/Next Loops Used to repeat statements in a loop a specific number of times Uses a numeric counter variable, called Loop Index, which is tested to determine the number of times the statements inside the loop will execute Loop Index is incremented at the bottom of the loop on each iteration. Step value can be included to specify the incrementing amount to increment Loop Index, step can be a negative number.

7. The For and Next Statements — General Form For LoopIndex [As DataType] = InitialValue To TestValue [Step Increment] ' Statements in loop. Next [LoopIndex] A For/Next loop can handle all three elements of a counter- controlled loop. Initialize the counter. Increment the counter. Test the counter to determine when it is time to terminate the loop.

8. For/Next Loop Diagram

9. Exiting Loops In some situations, you may need to exit the loop prematurely. Click on the form’s close box or use the VB menu bar or toolbar to stop the program; or Ctrl+Break. Use the Exit For statement inside the loop structure. Generally, the Exit For statement is part of an If statement.