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Learn the power of If-Then-Else instruction in CSE programming to streamline your code. Discover how to optimize conditional statements, factoring for readability and speed.
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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 • If not, perform instructions in ELSE clause
If Then Else Instruction • Reserved Words • IF • THEN • ELSE • Test Conditions • Same as if/then instruction
If Then Else Instruction • As with the if/then instruction, any number of instructions can be placed between the delimiters BEGIN & END
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!
If Then Else Instruction • Example IFnext-to-a-beeperTHEN BEGIN pickbeeper; END ELSE BEGIN putbeeper; END;
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
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;
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;
Writing Efficient Conditional Statements • Factoring • Example #1 • After factoring IFnext-to-a-beeperTHEN BEGIN pickbeeper; END ELSE BEGIN putbeeper; END; move;
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;
Writing Efficient Conditional Statements • Factoring • Example #2 • After factoring pickbeeper; IFnext-to-a-beeperTHEN BEGIN turnleft; END ELSE BEGIN move; END;
References • Richard E. Pattis (revised by Jim Roberts & Mark Stehlik), Karel the Robot, John Wiley & Sons, Inc., 2nd edition, 1995, pp 65-86