CSE 115. Introduction to Computer Science I

Transcription

1 CSE 115 Introduction to Computer Science I

2 Announcements Graded TopHat questions starts Fri. Sign up soon (& talk to us for help) Calling Function & Defining Function May need both lectures for UBInfinite exercises Even if you cannot finish, good idea to try starting work after class repl.it helps solve UBInfinite questions Only 1 st answer earns credit, so make it count Once code works, copy-and-paste answer back into UBInfinite

3 Help us help you! Search Piazza before posting: question might be answered When posting to Piazza: tell us what you think the problem is tell us what you've tried tell us where you're getting stuck Just posting a screenshot of code and saying 'help' isn't an effective learning strategy.

4 Help us help you! Search Piazza before posting: question might be answered When posting to Piazza: Tell us what YOU think problem is tell us what you've tried tell us where you're getting stuck Just posting a screenshot of code and saying 'help' isn't an effective learning strategy.

5 Help us help you! Search Piazza before posting: question might be answered When posting to Piazza: Tell us what YOU think problem is What you've tried to solve problem on your own tell us where you're getting stuck Just posting a screenshot of code and saying 'help' isn't an effective learning strategy.

6 Help us help you! Search Piazza before posting: question might be answered When posting to Piazza: Tell us what YOU think problem is What you've tried to solve problem on your own Explain which topic is confusing or hard-to-understand Just posting a screenshot of code and saying 'help' isn't an effective learning strategy.

7 Help us help you! Search Piazza before posting: question might be answered When posting to Piazza: Tell us what YOU think problem is What you've tried to solve problem on your own Explain which topic is confusing or hard-to-understand Developing good learning strategies is important part of class; upper-level classes (and bosses) need more than saying 'help'

8 Today's Plan Review Calling functions Final Ungraded TopHat Check Demo: function calls in Python

9 Variable Key Concept Name that has been assigned a value

10 Variables Assignment Statement name must appear on left-hand side of equal sign expression must appear on right-hand side of equal sign name = expression Starts by evaluating right-hand side of statement Variable then assigned value that was produced.

11 Variables in Expressions Variables also expressions After assigned value, variable usable as simple expression: x = 3 interesting_name = 6 interesting_name = x print(x * 5) school_name = 'UB' mascot = (school_name + " ") + "Bulls"

12 Expression Subgoals 1. Determine data type of all subexpressions 2. Check that data types usable in operation 3. Evaluate expression

13 Assignment Subgoals 1. Determine data type of all subexpressions 2. Check that data types usable in operation 3. Evaluate expression 4. Update variable's value

14 Today's Plan Calling functions

15 Functions Function is named block of code Execute code suite by calling the function Code a function call by typing name & providing arguments Good for common tasks, since can call function anytime

16 Functions Original Ideas From Math

17 Expressions Function Call Calling function like hiring it to have it step in & do its thing Function does all of work, you get any result it produces Function call is a complex expression: Function name is operation Argument(s) are subexpression(s)

18 Functions Python includes many built-in functions abs(num) min(num_1,num_2) max(num_1,num_2) pow(a_name,other_name) round(consistency_sucks) round(x,y) print(value_to_print)

19 Imports Also has functions defined in modules Must import module to use these functions import math Example using Python's math module hope_close_enough = math.sin( ) module_also_has_constants = math.pi/2 shorter = module_also_has_constants print( math.cos( shorter ) * 4 )

20 Function Call Subgoals 1. Determine whether function is built-in or in a module a) If in a module, check for import earlier in file 2. Write the function call 3. Determine whether arguments are appropriate a) Are there equal numbers of arguments & parameters? b) Is the type of each argument correct? 4. Determine if function returns a value & the type returned 5. Determine that the function value is used correctly

21 Function Calls Examples Expression pow starts with name of function min that should be executed abs print

22 Function Calls Examples ( 3, 2 ) Function call's ( 16/3, 4 ) arguments listed inside of (x) parentheses ( "Hi there!" )

23 Function Calls Examples pow( 3, 2 ) calculates 3 2 ; evaluates to value of 9 min( 16/3, 4 ) calculates minimum of 5⅓ & 4; evaluates to value of 4 x = -6 abs(x) calculates absolute value of -6; evaluates to value of 6 print( "Hi there!" )

24 Function Call Subgoals 1. Determine whether function is built-in or in a module a) If in a module, check for import earlier in file 2. Write the function call 3. Determine whether arguments are appropriate a) Are there equal numbers of arguments & parameters? b) Is the type of each argument correct? 4. Determine if function returns a value & the type returned 5. Determine that the function value is used correctly

25 Today's Plan Final Ungraded TopHat Check

26 Pick the True Statement Choose 1 statement which is true in Python: A. Only variables have types B. Variable can be assigned only once C.str literals can use either double (") or single (') quotes D.+ performs addition if both subexpressions are numbers & catenation if at least 1 is a str

27 Pick the True Statement Choose 1 statement which is true in Python: A. Only variables have types B. Variable can be assigned only once C.str literals can use either double (") or single (') quotes D.+ performs addition if both subexpressions are numbers & catenation if at least 1 is a str Convince Your Neighbor Your Answer Is Correct

28 Pick the True Statement Choose 1 statement which is true in Python: A. Only variables have types B. Variable can be assigned only once C.str literals can use either double (") or single (') quotes D.+ performs addition if both subexpressions are numbers & catenation if at least 1 is a str

29 Pick the True Statement Choose 1 statement which is true in Python: A. Only variables have types Only values have a type; variable provides "name" for location holding value temporarily

30 Pick the True Statement Choose 1 statement which is true in Python: Variables B. Variable can be assigned only once CAN be reassigned; just replaces what it's value is

31 Pick the True Statement Choose 1 statement which is true in Python: + does not combine a D. + performs addition if both subexpressions are numbers & catenation if at least 1 is a str number & a string

32 Pick the True Statement Choose 1 statement which is true in Python: But C.str literals can use either double (") or single (') quotes CANNOT use both in same literal

33 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 5 num = math.sin("180") 6 zero = abs(math.cos(math.pi)) 7 print(max(max(5, zero), smaller)) A. 1, 2, 3, 4, 5, 6, 7 D. 1, 3, 6, 7 B. 1, 2, 3, 4, 5, 7 E. 1, 2, 3, 4, 5 C. 1, 2, 3, 4, 6 F. No answers correct

34 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 5 num = math.sin("180") 6 zero = abs(math.cos(math.pi)) 7 print(max(max(5, zero), smaller)) Convince Your Neighbor Your Answer Is Correct A. 1, 2, 3, 4, 5, 6, 7 D. 1, 2, 3, 6, 7 B. 1, 2, 3, 4, 5, 7 E. 1, 2, 3, 4, 5 C. 1, 2, 3, 4, 6 F. No answers correct

35 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 5 num = math.sin("180") 6 zero = abs(math.cos(math.pi)) 7 print(max(max(5, zero), smaller)) A. 1, 2, 3, 4, 5, 6, 7 D. 1, 2, 3, 6, 7 B. 1, 2, 3, 4, 5, 7 E. 1, 2, 3, 4, 5 C. 1, 2, 3, 4, 6 F. No answers correct

36 Which Lines Legal? 1 import math A. 1, 2, 3, 4, 5, 6, 7 D. 1, 2, 3, 6, 7 B. 1, 2, 3, 4, 5, 7 E. 1, 2, 3, 4, 5 C. 1, 2, 3, 4, 6 F. No answers correct

37 Which Lines Legal? 1 import math 2 answer = A. 1, 2, 3, 4, 5, 6, 7 D. 1, 2, 3, 6, 7 B. 1, 2, 3, 4, 5, 7 E. 1, 2, 3, 4, 5 C. 1, 2, 3, 4, 6 F. No answers correct

38 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / A. 1, 2, 3, 4, 5, 6, 7 D. 1, 2, 3, 6, 7 B. 1, 2, 3, 4, 5, 7 E. 1, 2, 3, 4, 5 C. 1, 2, 3, 4, 6 F. No answers correct

39 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) A. 1, 2, 3, 4, 5, 6, 7 B. 1, 2, 3, 4, 5, 7 E. 1, 2, 3, 4, 5 C. 1, 2, 3, 4, 6 F. No answers correct

40 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 5 num = math.sin("180") 6 7 C. 1, 2, 3, 4, 6 F. No answers correct

41 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) 7 C. 1, 2, 3, 4, 6 F. No answers correct

42 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 math.cos(math.pi) 7 C. 1, 2, 3, 4, 6 F. No answers correct

43 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 math.cos(math.pi) π 7 C. 1, 2, 3, 4, 6 F. No answers correct

44 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 abs(math.cos(math.pi)) value of type float 7 C. 1, 2, 3, 4, 6 F. No answers correct

45 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) value that must be a number 7 C. 1, 2, 3, 4, 6 F. No answers correct

46 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) 7 C. 1, 2, 3, 4, 6 F. No answers correct

47 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) 7 print(max(max(5, zero), smaller)) C. 1, 2, 3, 4, 6 F. No answers correct

48 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) 7 max(5, zero) C. 1, 2, 3, 4, 6 F. No answers correct

49 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) 7 max(max(5, some number zero), smaller) C. 1, 2, 3, 4, 6 F. No answers correct

50 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) 7 print(max(max(5, a number that zero), has some smaller)) value C. 1, 2, 3, 4, 6 F. No answers correct

51 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) 7 print(max(max(5, zero), smaller)) F. No answers correct

52 Which Lines Legal? 1 import math 2 answer = 42 3 six = answer / 6 4 smaller = min(answer, six * 9) 6 zero = abs(math.cos(math.pi)) 7 print(max(max(5, zero), smaller)) F. No answers correct

53 Today's Plan Demo: function calls in Python

54 Function Call Subgoals 1. Determine whether function is built-in or in a module a) If in a module, check for import earlier in file 2. Write the function call 3. Determine whether arguments are appropriate a) Are there equal numbers of arguments & parameters? b) Is the type of each argument correct? 4. Determine if function returns a value & the type returned 5. Determine that the function value is used correctly