CSE 115. Introduction to Computer Science I

Transcription

1 CSE 115 Introduction to Computer Science I

2 Progress In UBInfinite? A. Haven't started B. Earned 3 stars in "Calling Functions" C. Earned 3 stars in "Defining Functions" D. Earned 3 stars in "Conditionals" E. Earned 1+ stars in "Module 1 PreLab" F. Earned 3 stars in "Module 1 PreLab"

3 Announcements Lab exam #1 in labs next week Need 3 stars on Python's Module 1 PreLab Available for first 55 minutes of lab Only students taking Lab Exam allowed in Baldy 21 If you want paper, UTA can provide blank sheets Bring your own pens/pencils; UTAs cannot share

4 Announcements For lab exam #1: Will need to write 3 short Python functions 1 st function should be simple 2 nd & 3 rd functions slightly more complex

5 Today's Plan Review Functions and control flow

6 Selection Statement: if Parts Of if Statement Header if keyword guard expression if a < b and a < c

7 Execution Path When Expression is True x = 12 y = 14 if z < y : z = x print(z)

8 Execution Path When Expression is False x = 12 y = 14 if z < y : print(z)

9 After if Statement print(z) Code after if statement ALWAYS executed

10 Selection Statement: if-elif-else

11 Selection Statement: if-elif-else Parts of an if-elif-else Statement if header delimiter elif header else header if a < b and a < c : print('a is the smallest') smallest = a elif b < a and b < c : print('b is the smallest') smallest = b else : print('c is the smallest') smallest = c if body delimiter elif body delimiter else body

12 Selection Execution Subgoal 1. Determine if the guard expression evaluates to True or False 2. If expression evaluates to True, run the code suite. When code suite finishes, skip to the first statement after the selection statement If expression evaluates to False, skip past the code suite

13 Execution Path When a is 5, b is 7, c is 5.2 if a < b and a < c : print('a small') sm = a print(sm)

14 Execution Path When a is 5, b is 6, c is 4.5 if a < b and a < c : elif b < c and x == 2 : else : print('weird') z = c print(sm)

15 Which Control Flow Shows an If-Elif-Else? a) b) c) d)

16 Which Control Flow Shows an If-Elif-Else? a) b) c) d)

17 Selection Writing Subgoals 1. Determine number of distinct paths needed 2. For each path, write guard expression for when that path should be executed a) List guard expressions in order from the most-restrictive to least-restrictive 3. Write the if(-elif)(-else) statement

18 Selection Statements if-elif-elif-elif No limit on number of elifs you can add Boolean expressions can be anything; no relationship required No restrictions to suites; do not need to be related else also optional, but if used else must be after the elifs Python jumps to end once suite run; at most 1 if/elif/else run

19 Today's Plan Functions and control flow

20 Function in Math Want function which takes in a single input. The function should return the sum of: the input squared; the input multiplied by 5; and the number 2. f x =

21 Function in Math Want function which takes in a single input. The function should return the sum of: the input squared; the input multiplied by 5; and the number 2. f x = x 2 + 5x + 2

22 Math to Python Now want to write this as a Python function def f(x): f x = x 2 + 5x + 2

23 Math to Python Now want to write this as a Python function f x = x 2 + 5x + 2 def f(x): return (x ** 2) + (x * 5) + 2

24 Smaller (of 2) Want function which returns smaller param (For purposes of this exercise, cannot use built-in min() function) Work with neighbors and be prepared to: explain your answer (in English) & show steps involved (in control flow)

25 Smaller (of 2) Want function which returns smaller param (For purposes of this exercise, cannot use built-in min() function) Work with neighbors and be prepared to: explain your answer (in English) & show steps involved (in control flow)

26 Smaller (of 2) One possible solution (in Python): def smaller(x, y):

27 Smaller (of 2) One possible solution (in Python): def smaller(x, y): if ( x < y ) : else :

28 Smaller (of 2) One possible solution (in Python): def smaller(x, y): if ( x < y ) : return x else :

29 Smaller (of 2) One possible solution (in Python): def smaller(x, y): if ( x < y ) : return x else : return y

30 Smaller (of 2) One possible solution (in Python): def smaller(x, y): if ( x < y ) : return x else : return y

31 Smaller (of 2) One possible solution (in Python): def smaller(x, y): if ( x < y ) : return x else : return y Mistakes happen; critical to verify code works smaller(4, 5) has value 4 smaller(5, -1) has value -1 smaller(8, 8) has value 8

32 Smaller (of 2) One possible solution (in Python): def smaller(x, y): if ( x < y ) : return x else : return y Mistakes happen; critical to verify code works smaller(4, 5) has value 4 smaller(5, -1) has value -1 smaller(8, 8) has value 8

33 Smallest (of 3) Function which returns smallest params (For learning purposes, min() still banned) Work with neighbors and be prepared to: explain your answer (in English) & show steps involved (in control flow)

34 Smallest (of 3) Function which returns smallest params (For learning purposes, min() still banned) Work with neighbors and be prepared to: explain your answer (in English) & show steps involved (in control flow)

35 Smallest (of 3) One possible solution (in Python): def smallest(x, y, z): if (x <= y <= z or x <= z <= y) : return x elif (y <= x <= z or y <= z <= x) : return y else : return z

36 Smallest (of 3) One possible solution (in Python): def smallest(x, y, z): if (x <= y <= z or x <= z <= y) : return x elif (y <= x <= z or y <= z <= x) : return y else : return z

37 Smallest (of 3) One possible solution (in Python): def smallest(x, y, z): if (x <= y <= z or x <= z <= y) : return x elif (y <= x <= z or y <= z <= x) : return y else : return z I lied; I do not like to live dangerously

38 Smallest (of 3) One possible solution (in Python): def smallest(x, y, z): if (x <= y <= z or x <= z <= y) : return x elif (y <= x <= z or y <= z <= x) : return y else : return z I lied; I do not like to live dangerously smallest(4, 395, 7) has value 4 smallest(1, 0, 74) has value 0 smallest(-1, -2, -3) has value -3

39 Smallest (of 3) "Code golf" solution def smallestv2(x, y, z): return smaller(smaller(x, y), z)

40 Smallest (of 3) "Code golf" solution