1. EGR 115 Introduction to Computing for Engineers Branching & Program Design – Part 3 Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers

2. Lecture Outline Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Branches Slide 2 of 16

3. Branching & Program Design Branches – Program Flow Control Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Program Control Flow  Refers to the order in which each statement of a program is executed  Sequential Flow (prior Chapters) o Simple top to bottom no branches!!  Line #1, line #2, …, last line.  Logical Branching (Current Chapter) o Program flow based on Branching via Logical comparisons  E.g., if, switch, try, break, …  Looping (Next Chapter) o Conditional repetative execution of statements  For, while, … Slide 3 of 16

4. Branching & Program Design Branches – The if Statement Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers There are 3 forms of the if statement if (Logical Expression) statement(s) end if (Logical Expression) statement(s) else other statement(s) end Slide 4 of 16

5. Branching & Program Design Branches – The if Statement Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers There are 3 forms of the if statement if (Logical Expression1) statement(s) elseif (Logical Expression2) other statement(s) elseif (Logical Expression3) other statement(s). else other statement(s) end Slide 5 of 16......

6. Branching & Program Design Branches – A 1 st Example: The Guessing Game Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers An Example: The Guessing Game  Problem: o I am thinking of an integer between 1 and 10 o Can you guess what number I am thinking of? Lets go through the 5 Step Top-Down Design Procedure Step 1: Clearly state the problem  Use the computer to randomly generate an integer 1  number  10  Prompt the user for a guess at the number  Respond to the guess Slide 6 of 16

7. Branching & Program Design Branches – A 1 st Example: The Guessing Game Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Step 2: Define inputs and outputs Step 3: Design the Algorithm (pseudocode)  Generate a random integer: 1  num  10  Prompt the user to guess the number  Test the guess and issue a response My Program guess Response Integer Text string Slide 7 of 16

8. Branching & Program Design Branches – A 1 st Example: The Guessing Game Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Step 4: Convert the Algorithm into Code % Generate a random integer: 1 <= num <= 10 num = rand; % Generate a random number betw 0 & 1 num = ceil(10*num); % Convert to an integer betw 1 & 10 % Prompt the user to guess the number guess = input('Guess a Integer from 1 to 10: '); % Test the guess and issue a response if guess == num disp('Your Guess is Correct!!'); else disp('Your Guess is NOT Correct!!') end Step 5: Test the resulting program Could use randi(10) Guessing_Game_v1.m Slide 8 of 16

9. Branching & Program Design Branches – A 1 st Example: The Guessing Game Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Let’s Modify the program to provide a “better” response % Test the guess and issue a response of Correct, % too high, or too low if guess < num disp('Your Guess is Too Low!!'); elseif guess > num disp('Your Guess is Too High!!'); else disp('Your Guess is Correct!!') end Notice that only one of the conditional blocks will ever get processed!! Could use another elseif => Less Efficient What if the user entered a non-integer? Guessing_Game_v2.m Slide 9 of 16

10. Branching & Program Design Branches – A 1 st Example: The Guessing Game Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers We could also use nested if structures: % Test the guess and issue a response of Correct, % too high, or too low if guess < num disp('Your Guess is Too Low!!'); else if guess > num disp('Your Guess is Too High!!'); else disp('Your Guess is Correct!!') end It is good programming practice to indent code Guessing_Game_v3.m Slide 10 of 16

11. Branching & Program Design Branches – A 2 nd Example: Converting to Letter Grades Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers An Example: Convert Numeric Grades to Letter Grades  Given a numeric grade determine the letter equivalent. Step 1: Clearly state the problem:  Given the relationship between numeric and letter grades as: o Numeric Grade ≥ 90 is an A o 80 ≤ Numeric Grade < 90 is an B o 70 ≤ Numeric Grade < 80 is an C o 60 ≤ Numeric Grade < 70 is an D o Numeric Grade < 60 is an F  Prompt the user for a numeric grade  Respond with the letter grade equivalent Slide 11 of 16

12. Branching & Program Design Branches – A 2 nd Example Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Step 2: Define inputs and outputs Step 3: Design the Algorithm (pseudocode)  Prompt the user for the numeric grade  Determine and respond with the letter grade equivalent My Program grade Response float Text string Slide 12 of 16

13. Branching & Program Design Branches – A 2 nd Example Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Step 4: Convert the Algorithm into Code % Prompt the user for the numeric grade numeric_grade = input('Enter the Numeric Grade (0-100): '); % Convert a numeric grade to a letter Grade if numeric_grade < 60 disp('Letter Grade = F'); elseif numeric_grade < 70 disp('Letter Grade = D'); elseif numeric_grade < 80 disp('Letter Grade = C'); elseif numeric_grade < 90 disp('Letter Grade = B'); else disp('Letter Grade = A') end What happens if the numeric grade entered is greater than 100? Let’s analyze the program’s behavior in the debugger. Numeric_Grade_Converter_v1.m Slide 13 of 16

14. Branching & Program Design Branches – A 2 nd Example Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Step 5: Test the resulting program  What if the user provides an invalid input? o Approach #1: Trap all possible errors  Create a variable to denote if error and type of error » E.g., Error_Var = 0 (no error) or = 1 (wrong type) or …  If no error (Error_Var = 0) continue as usual  if error found, print message identifying the type of error » Some types can be “fixed,” then continue, others not, then stop. o Approach #2:  If an error is found terminate execution and print “Error Found – Terminating Execution” o Approach #3:  If an error is found prompt the user to re-enter the input Slide 14 of 16

15. Branching & Program Design Branches – A 2 nd Example Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers Trapping invalid input entries – Approach #1 % Prompt the user for the numeric grade numeric_grade = input('Enter the Numeric Grade (0-100): '); % Check the input for validity assuming the input is numeric if ~isscalar(numeric_grade) % Detect non-scalar entry disp('You have entered a non-scalar Grade'); valid_input = false; elseif numeric_grade < 0 % Detect out of bounds entry: < 0 disp('You have entered a negative Grade'); valid_input = false; elseif numeric_grade > 100 % Detect out of bounds entry: > 100 disp('You have entered a Grade of > 100'); valid_input = false; else valid_input = true; end Numeric_Grade_Converter_v2.m Slide 15 of 16

16. Next Lecture Friday 03 Oct 2014 EGR 115 Introduction to Computing for Engineers More Branching More Debugging Slide 16 of 16