1. Karel J Robot
Chapter 6

2. Iteration (Loops) Loops repeat a set of instructions
Two types of loops:
Definite loops ( for ) perform instructions explicit number of times
Indefinite loops ( while ) perform instructions an indefinite number of times (until a certain test fails)
Chapter 6

3. for Loops
General form: for ( <initialize variable>; <test>; <increment> ) { <instruction set> }
Chapter 6

4. for Loops (cont.)
<initialize variable> sets a variable/identifier to a certain value (variable is usually count, i, j)
<test> is a test that is evaluated each time the body is about to be executed (when false, loop is exited)
<increment> changes the loop control variable (usually x++ or x--)
Chapter 6

5. for Loops (cont.)
Example: for (int x=1; x<=5; x++) { karel.move(); }
This causes karel to move 5 times
Chapter 6

6. for Loops (cont.) Flow of for loops: Initialization statement executes
If test is true, proceed to step 3; if test is false, go to step 6
Instructions in body of loop are executed
Increment statement executes
Return to step 2
Program proceeds to statements after loop
Chapter 6

7. while Loops
General form: while ( <test> ) { <instruction list> }
Loop continues until test is false
Chapter 6

8. while Loops (cont.)
Example: while (karel.frontIsClear ()) { karel.move (); }
Causes karel to move continuously until there is a wall in front of it
Chapter 6

9. while Loops (cont.) Flow of while loops
If test is true, proceed to step 2; if test is false, go to step 4
Instructions in body of loop are executed
Go to step 1
Statements after loop are executed
Chapter 6

10. Building a While Loop
Step 1 – Identify what is true when the loop is finished (this is always easier than determining what is false while it is still executing)
Step 2 – Use the opposite form of step 1’s result as the <test> for the loop. You just need to negate the entire thing.
Chapter 6

11. Building a While Loop (cont’d)
Step 3 – make progress toward the goal (completion of the loop) within the loop
Step 4 – Do whatever is required before and/or after the loop to ensure that we solve the given problem
Example: Pick all beepers from a corner without knowing how many there are.
Chapter 6

12. Infinite Loops
In a for or while loop, it is possible for the test to never be false
When this happens, the loop continues infinitely
Depending on the compiler, application, and other circumstances, an error may occur or the app may crash
Chapter 6

13. Chapter 6