⇒ DS 2001 — CS Programming Practicum Fall 2020 — Felix Muzny mins ! a few we'll start in Practicum 2: Conditionals, For Loops, etc x = 12 if x > 10: What is the output of the given code? print("orange") - xouihftexs # to ← A. orange elif x > 0: B. orange → grapefruit print("grapefruit") C. grapefruit else: - D. grapefruit lemon print("lemon") - E. lemon 1
Logical Expressions • why "==" and not "=" to test for equality? X==5 5=-5 x Is - S - S x - s - - Yg yet - y A. python is just trying to be tricky B. "==" will test to see if two values are the same and "=" will test to see if the values stored in two variables are the same - - C. the premise of this question is wrong—you can use "=" to test for equality - assignment operator O D. "=" is has a di ff erent meaning in python code 2
Logical Expressions • What are the results of evaluating the following logical expressions? - D True • 5 != 7 F T ) → False • 13.2 > 6.6 and 6.6 < 3 ) ( ( T F → True • 13.2 > 6.6 or 6.6 < 3 D False { • 'a' == 'apple' - - - → True • 'a' < 'g' own ! • 'A' < 'g' - b tent out on your 3
Conditionals: in "pseudocode" ⑦ if • We want to write a program that: e , • asks the user for a number • if the number is larger than 1000, tell them that they picked a big 2) number 3) • when the program finishes, displays a message telling the user that the program is done 4
Conditionals: in "pseudocode" if lela • We want to write a program that: : • asks the user for a number • if the number is larger than 1000, tell them that they picked a big number • otherwise, tells them that they did not pick a big number 3 4 • when the program finishes, displays a message telling the user that the program is done 5
Conditionals: in "pseudocode" ask the user for a number else tell them that it's big tell them that it's not big tell them that the program has finished running 6
Conditionals • We incorporate logical expressions into code with conditionals (also called "selection statements") • Our first example of a conditional is an "if" statement if logical expression: T # code to run if the logical expression # evaluates to True # notice indent! • All conditionals evaluate logical expressions to a boolean value ( True or False ) 7
⇐ Conditionals • If we want to run certain code in one case and other code in all other cases, we will you an "if/else" statement if logical expression: O # code to run if the logical expression # evaluates to True # notice indent! else: # code to run if the logical expression # evaluates to False 8
Conditionals • If we have more than two branches, we'll use an if/elif/else structure if 688 if logical expression 1: # code to run if the logical expression 1 # evaluates to True lot # notice indent! on :& elif logical expression 2: # code to run if the logical expression 1 evaluates to False # and logical expression 2 evaluates to True 0¥ else: # code to run if the logical expression # evaluates to False 9
For Loops • All loops are used to repeat code. We may want to do the same task over and over, and we may want to do a very similar task over and over. • Flip a coin 10 times • Remind your roommate to do the dishes once for each dish left in the sink • Count from 1 to 100 10
For loops: in "pseudocode" • We want to write a program that: H • asks the user for their age 2) • prints out "happy birthday" the same number of times as their age 3) • when the program finishes, displays a message telling the user that the program is done 11
For loops: in "pseudocode" 1) ask the user for their age print out "happy birthday" 2) x the user 's age 3) tell them that the program has finished running 12
For Loops for variable_name in something_we_can_loop_over: → # code that we want repeated # code to run when we're done • For loops are used (as opposed to while loops) when we know ahead of time how many times the loop needs to repeat: times = 5 # I know now how many times to repeat for time_number in range(times): & print("repetition!") S print("all done!") 13
For Loops • The number of times might be hardcoded , come from the user , be a programmatically generated value , or be the length of a list (as a few examples) times = int(input("times? ")) # I know now how many times to repeat for time_number in range(times): Eri print("repetition!") print("all done!") : yhiatu.is to investigate thebe ! got no 14
For loops • How many times does the given for x D2 x = 10 loop run? y = -3 F T if x < 100 and y > 0: A. 10 x = 5 B. 5 elif x > 0 or y > 0: C. 2 x = 2 D. -3 → for time_number in range(x): print("repetition!") 15
Practicum today • You'll be working with random numbers today • This is how we can simulate a wide variety of coin, dice, and card games! • (you also won't know what value they have until you run your programs!) • Fun facts about random numbers: • Truly random numbers are surprisingly di ffi cult for computers to generate • the random module in python generates "pseudorandom" numbers • It uses the current time of your computer as a starting "seed" number to generate what appears to be a sequence of random numbers. 16
Practicum today • We'll code up one of the problems together around 15 minutes before the - 1 : 10 end of practicum today! • Those of you who are remote—you'll be in breakout rooms. Anuj, Satya and myself will be rotating between the rooms. • Use the "ask for help" button if one of us isn't there and you need some help • Please choose one person to screen share in your breakout room. You'll - all submit code individually, but we want you to discuss the problems and work together. 17
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