The document summarizes a programming class lecture on repetition using while and for loops. It provides examples of printing numbers from 1 to 10 using a while loop, and discusses how to properly increment the counter variable. It then shows that a while loop can be written as a for loop for brevity. Nested for loops are demonstrated to count down and print "SPLASH!". An exercise is proposed to have students simulate loop execution by assigning roles.

1. Introduction to Programming
Class 4
Paul Brebner

2. Housekeeping
• The Programming course shared directory is
located at XXX. I’ll update this with information,
sub directories are:
– Exercises
– Lessons
– Textbook
– Students
• The processing environment has a shortcut on
desktops, so you won’t need to reinstall it again.

3. Repetition (of repetition!)
• What does this program do?
println(“1”);
println(“2”);
println(“3”);
println(“4”);
println(“5”);
println(“Once I caught a fish alive”);
println(“6”);
println(“7”);
println(“8”);
println(“9”);
println(“10”);
println(“Then I let it go again (etc)”);

4. Repetition (of repetition!)
• This
1
2
3
4
5
Once I caught a fish alive
6
7
8
9
10
Then I let it go again (etc)

5. Using a while loop
with 2 bugs
int number = 1; // start from 1
while (number <= 10) // while number <= 10 repeat the block
{ // a block – do everything between { and }
println(number); // print the number each time
println(“Once I caught a fish alive”);
println(“Then I let it go again (etc)”);
}

6. Repetition (of repetition!)
1
Once I caught a fish alive
Then I let it go again (etc)
1
Once I caught a fish alive
Then I let it go again (etc)
1
Once I caught a fish alive
Then I let it go again (etc)
1
Once I caught a fish alive
Then I let it go again (etc)
1
Once I caught a fish alive
Then I let it go again (etc)
...

7. Using a while loop
int number = 1; // start from 1
while (number <= 10) // while number <= 10 repeat the block
{ // a block – do everything between { and }
println(number); // print the number each time
println(“Once I caught a fish alive”);
println(“Then I let it go again (etc)”);
number = number + 1; // must increment number by 1 each time
}

8. Better - slightly
1
Once I caught a fish alive
Then I let it go again (etc)
2
Once I caught a fish alive
Then I let it go again (etc)
3
Once I caught a fish alive
Then I let it go again (etc)
4
Once I caught a fish alive
Then I let it go again (etc)
5
Once I caught a fish alive
Then I let it go again (etc)
...
10
Once I caught a fish alive
Then I let it go again (etc)

9. Using a while loop
and an if
int number = 1; // start from 1
while (number <= 10) // while number <= 10 repeat the block
{ // a block – do everything between { and }
println(number); // print the number each time
if (number == 5)
println(“Once I caught a fish alive”);
else
if (number == 10)
println(“Then I let it go again (etc)”);
number = number + 1; // must increment number by 1 each time
}

10. Correct
1
2
3
4
5
Once I caught a fish alive
6
7
8
9
10
Then I let it go again (etc)

11. for loop
this while loop is identical to for loop
int number = 1; // start from 1
while (number <= 10) // while number <= 10 repeat the block
{ // a block – do everything between { and }
println(number); // print the number each time
if (number == 5)
println(“Once I caught a fish alive”);
else
if (number == 10)
println(“Then I let it go again (etc)”);
number = number + 1; // must increment number by 1 each time
}

12. for loop
// start from 1
// while number <= 10 repeat the block
// at end increment number by 1 and repeat
for (int number = 1; number <= 10; number = number + 1)
{
println(number);
if (number == 5)
println(“Once I caught a fish alive”);
else
if (number == 10)
println(“Then I let it go again (etc)”);
}

13. comparison
// while loop
int number = 1; // start from 1
while (number <= 10) // while number <= 10 repeat the block
{ // a block – do everything between { and }
println(number); // print the number each time
if (number == 5)
println(“Once I caught a fish alive”);
else
if (number == 10)
println(“Then I let it go again (etc)”);
number = number + 1; // must increment number by 1 each time
}
// for loop
for (int number = 1; number <= 10; number = number + 1)
{
println(number);
if (number == 5)
println(“Once I caught a fish alive”);
else
if (number == 10)
println(“Then I let it go again (etc)”);
}

14. number++
// start from 1
// while number <= 10 repeat the block
// at end increment number by 1 and repeat -> number++
for (int number = 1; number <= 10; number++)
{
println(number);
if (number == 5)
println(“Once I caught a fish alive”);
else
if (number == 10)
println(“Then I let it go again (etc)”);
}

15. What does this version do?
For loops can be NESTED
for (int number = 1; number <= 10; number++)
{
println(number);
if (number == 5)
println(“Once I caught a fish alive”);
else
if (number == 10)
{
println(“Then I let it go again (etc)”);
for (int countDown = 10; countDown >= 0; countDown--)
println(countDown);
println(“SPLASH!”);
}
}

16. 1
2
3
4
5
Once I caught a fish alive
6
7
8
9
10
Then I let if go again (etc)
10
9
8
7
6
5
4
3
2
1
0
SPLASH!

17. Simulation (using humans) exercise
• Need roles for
– For (control)
– Initialisation
– Condition
– End action
– Println number
– If/else
– Number == 5
– Println Once I ...
– Number == 10
– println Then I ...

18. Roles highlighted in different colours
for (int number = 1; number <= 10; number++) // roles 1, 2, 3, 4
{
println(number); // role 5
if (number == 5) // role 6 7
println(“Once I caught a fish alive”); // role 8
else // role 5
if (number == 10) // role 5 9
println(“Then I let it go again (etc)”); // role 10
}
• Line up in order
• For is the controller (keeps track of what to do next) order is 1, 2, 3, (not 4), 5-10, then
4, and back to 3 (not 20, 5-10, etc.
• Println writes on whiteboard
• Variable declaration, assignment, conditions (<= and ==), and maths (e.g. ++) change or
check variable value on whiteboard

19. Exercises
• Textbook
– Page 42ff
– Example 4.6 to 4.13
– Then go back to fruit bowl problem
– Save your fruit bowl problem to work on later
– Next time Robot 2 Page 49