1. FLUENCY WITH INFORMATION TECNOLOGY
Skills, Concepts, and Capabilities

2. PART 4
Problem Solving

3. chapter21
ONCE IS NOT ENOUGH
Iteration Principles

4. ITERATION: PLAY IT AGAIN, SAM
What is a loop?
A loop is a programming structure that provides a means of repeating the same code multiple times.
The programmer must control the loop.
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5. Classic Loop Problem Instructions on a bottle of shampoo. Lather Rinse
Repeat
But when does it end? Repeat once, twice, each time we hit repeat?
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6. Loop components There are four parts to every loop initialization
decision
body
update
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7. Loop control
In most loops, there will be one variable that will control the loop.
That variable is called the loop control variable.
The loop control variable must be initialized and updated.
The loop continues until the loop control variable reaches a predefined value.
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8. Initialization
We set our loop control variable to some beginning value that makes sense for the task.
Counting tasks, set the variable to 0 or 1.
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9. Update
Each time through the loop, the loop control variable may be changed.
This change is usually called an increment, but there are many ways to control loops that do not involve an increment.
This update must “help” the loop control variable to reach the control value.
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10. Decision A decision is like the condition of an if statement.
If the condition is true, the loop continues to run.
If the condition is false, the loop stops and the statement just beneath the loop executes.
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11. Body The action or set of actions that you want to repeat.
The body of a loop may include update or it may simply carry out an action.
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12. The World Famous Iteration
for loop
for loops are found in most programming languages
a for loop is a counting loop also called a definite loop
a for loop contains all four parts of a loop
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13. The for Statement – aka counting loop
A for statement has the following syntax:
The initialization
is executed once
before the loop begins
The statement is
executed until the
condition becomes false
for ( initialization ; condition ; increment ) {
statement(s); }
The increment portion is executed at the end of each iteration
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14. Let’s look at Counter.html
Simple counting loop.
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15. Let’s look at two loops Counter2.html
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16. Loop problems
Infinite loop. The loop control variable fails to reach the limit value.
Caused by failing to update the loop control variable or failing to have the loop control variable reach the limit.
May also occur if you have a value that “skips” over the limit.
Demo
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17. Off by one error
Have your program increment one too many or one too few times.
Demo
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