1 / 13

CSE 111

CSE 111. Karel the Robot. If Then Else Instruction. Format If condition THEN BEGIN instruction(s) END ELSE BEGIN instruction(s) END; How does it work? If condition is met, then perform instructions in THEN clause

hideaki-oota
Download Presentation

CSE 111

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CSE 111 Karel the Robot

  2. If Then Else Instruction • Format If condition THEN BEGIN instruction(s) END ELSE BEGIN instruction(s) END; • How does it work? • If condition is met, then perform instructions in THEN clause • If not, perform instructions in ELSE clause

  3. If Then Else Instruction • Reserved Words • IF • THEN • ELSE • Test Conditions • Same as if/then instruction

  4. If Then Else Instruction • As with the if/then instruction, any number of instructions can be placed between the delimiters BEGIN & END

  5. If Then Else Instruction • Notice how the semicolon after END indicates the end of the if/then/else statement • If/then • Semicolon after END • If/then/else • Semicolon after second END!

  6. If Then Else Instruction • Example IFnext-to-a-beeperTHEN BEGIN pickbeeper; END ELSE BEGIN putbeeper; END;

  7. Nested If Statements • If/then or if/then/else statements written within the then or else clause of another instruction • Used for more complex tests • Avoid nesting more than one level deep to keep programs readable

  8. Nested If Statements • Example • Task • Pick up two beepers • Ensure that if there are not two beepers on the intersection Karel is standing on, the program will NOT end in an error shutoff • Code IFnext-to-a-beeperTHEN BEGIN pickbeeper; IFnext-to-a-beeperTHEN BEGIN pickbeeper; END END;

  9. Writing Efficient Conditional Statements • Factoring • Programs can be made more readable by removing redundant instructions from inside a conditional statement to outside the statement • It also reduces size of program • Can lead to faster runtimes since memory accesses are reduced • Example #1 • The following code fragment can be factored IFnext-to-a-beeperTHEN BEGIN pickbeeper; move; END ELSE BEGIN putbeeper; move; END;

  10. Writing Efficient Conditional Statements • Factoring • Example #1 • After factoring IFnext-to-a-beeperTHEN BEGIN pickbeeper; END ELSE BEGIN putbeeper; END; move;

  11. Writing Efficient Conditional Statements • Factoring • Example #2 • The following code fragment can be factored IFnext-to-a-beeperTHEN BEGIN pickbeeper; turnleft; END ELSE BEGIN pickbeeper; move; END;

  12. Writing Efficient Conditional Statements • Factoring • Example #2 • After factoring pickbeeper; IFnext-to-a-beeperTHEN BEGIN turnleft; END ELSE BEGIN move; END;

  13. References • Richard E. Pattis (revised by Jim Roberts & Mark Stehlik), Karel the Robot, John Wiley & Sons, Inc., 2nd edition, 1995, pp 65-86

More Related