1. CSC 160 Computer Programming for Non-Majors Lecture #3a: Stepper, Words, Sentences (continued) Prof. Adam M. Wittenstein Wittenstein@adelphi.eduhttp://www.adelphi.edu/~wittensa/csc160/

2. The Debug Button Last class, I said the Simply Scheme mode does not have a Stepper. There is actually a Debug button in place of the Step button. It is not as great, but still helpful. Let’s look at two examples from last class using Debug:

3. The Debug Button (+ 3 (* 4 5)) Step One: (* 4 5) = 20 Step Two: (+ 3 (* 4 5)) = 23 (item 4 (item 3 ‘(Today is Thursday September Seven))) Step One: (item 3 ‘(Today is Thursday September Seven))) = Thursday Step Two: (item 4 (item 3 ‘(Today is Thursday September Seven))) = r

4. Questions from Simply Scheme Do 5.3 on page 66. Do 5.3 on page 66. Do 5.11 on page 67. Do 5.11 on page 67.

5. Solutions to Questions 5.3 and 5.11 5.3: (first ‘mezzazine) = m *Returns the first letter of the word. (first ‘(mezzazine)) = ‘mezzazine *Returns the first word of the sentence. 5.11: For last to return a word, it needs to be given a sentence that ends with a word. For last to return a sentence, it needs to be given a sentence that ends with a sentence.

6. REVIEW: Converting from math notation to Scheme notation 1)Expand abbreviations 2)Parenthesize all subexpressions that have an operator. Should end up w/same number of operators, left-parentheses, and right-parentheses. 3)Move each operator to just after its own left parenthesis. 3z becomes 3 * z b 2 becomes b * b 3*3+4*5 becomes ( (3 * 3) + (4 * 5) ) b 2 - 4ac becomes ( (b * b) - (4 * a * c) ) ( (3 * 3) + (4 * 5) ) becomes ( + (* 3 3) (* 4 5) ) ( (b * b) - (4 * a * c) ) becomes (- (* b b) (* 4 a c) )

7. Translation Exercise 3x - 6/x 3x - 6/x √(b 2 -4ac) √(b 2 -4ac)

8. What’s on the Quiz? Atomic (Simple) Data Types –numbers, words, sentences, booleans Expressions / Calling Functions –subexpression: an expression inside of another expression. Vocabulary –function, argument, return value

9. What functions may be on the quiz? Numbers – +, -, *, / Words and sentences: –first, last, butfirst (bf), butlast –item, every, member?, vowel? –keep, word, sentence

10. Types of Quiz questions Translate a mathematical expression into Scheme. Translate a Scheme expression into math notation. Translate an expression about words or sentences into Scheme. Explain what a Scheme function on words or sentences means. Step through a problem (with numbers, words, or sentences) using the approach of your choice: Stepper, Debug, Little People

11. III. Preparing for Next Class

12. Next time… We will call functions involving pictures. Then, time permitting, we will see how to define variables. We will have a 20-25 minute quiz at the end of class.