CS 177 Week 6 Recitation Slides

1. CS 177 Week 6 Recitation Slides Review for Midterm Exam

2. Announcements

3. Question 1 • sum = 0   • x = 10   • while x > 1 :   • sum = sum + x   • x = x - 3   • print (sum) Q1. Which numbers are printed by the following loop: (A) 22 (B) 21 (C) 0 (D) 20

4. Question 1 • How many iterations in total? • After 1st iteration, x=7 • After 2nd , x=4 • After 3rd, x=1 • Then exit the loop • What is the value of sum in each iteration? • After 1st, sum=0+(x=10)=10 • After 2nd, sum=10+(x=7)=17 • After 3rd, sum=17+(x=4)=21

5. Question 2 • def fun(a, b, c): • if (a < b or c[0] == "A"): • if(a < 0 and c[0] == "B"): • return a + b • else: • print (a - b ) • else: • return -1 Q2. Consider the following code snippet. What is the output of calling: fun(10, 20, “BOB”)? (A) -10 (B) 30 (C) -1 (D) 0

6. Question 2 • After the function call, input arguments are initialized as follows: • a= 10, b=20, c=“BOB” • For 1st if statement, since a<b is True, the expression is True • Then it evaluates if(a < 0 and c[0] == "B"): • It is False since a<0 is False • Then print a-b will be executed • Result is -10

7. Question 3 def integerDecision(number): if number <=0: print("Input number is not positive.") elif number < 50 and number > 0: print("Input number is less than 50.") elif number >=50 and number<=100: if number == 60: print("I FOUND 60.") else: print("Input number ",number, " is >= 50 and <=100") elif number > 100: print("Input number is greater than 100.") else: print("It's a strange number.") Lab 5 solution

8. Question 3 if number <=0: print("Input number is not positive.") elif number < 50 and number > 0: print("Input number is less than 50.") #TODO 1.01 #Test if the input number is less than or equal to 0 #TODO 1.02 #Test if the input number is less than 50

9. Question 3 elif number >=50 and number<=100: if number == 60: print("I FOUND 60.") else: print("Input number ",number, " is >= 50 and <=100") #TODO 1.03 #Test if the input number is greater than or equal to 50, and less than or equal to 100, but not equal to 60 #1.04 #Inside the condition of 1.03, test if the number is equal to 60

10. Question 3 elif number > 100: print("Input number is greater than 100.") else: print("It's a strange number.") #TODO 1.05 #Test the input number is greater than 100

11. Question 4 Q8. Which of the following statements produce the same output? 1) print (11 + (13.0/2) + 2.5) 2) print (11 + 13//2 + 2.5 ) 3) print (11 + 13/2.0 + 2.5 ) 4) print ((11 + 13)/2.0 + 2.5) (A) 1), 2) and 3) (B) 1) and 2) (C) 1) and 3) (D) None of the above.

12. Question 4 First equation evaluates to 20 Second equation evaluates to 19.5 (13/2=6) Third equation evaluates to 20 Fourth equation evaluates to 14.5 Python will cast an int to double if the int is doing arithmetic operations (+,/,*,-) with another double value. Integer division will not round

13. Question 5 • myList = [0,1,2,3,4] • myString = “ hello” • 1) mylist[len(mylist)] • 2) b + 6 = 17 • 3) c = "Hello" + "World" • 4) myString[2] = ‘j’ Q9. Which of the following statements (1-4 below) generate an error? (A) 1), 2) and 4) (B) 1) and 2) (C) 1) and 4) (D) 1), 2), 3) and 4)

14. Question 5 mylist[len(mylist)] will throw an error, since the valid index will be 0 to len(mylist)-1 b + 6 = 17 is wrong since there cannot be an expression on the assignment left hand side myString[2] = ‘j’ is wrong since you cannot change a python string

15. Question 6 • a = 15 • b = 13 • c = 12 • d = 6 • e = 10 • if (a>b and d>4) or (e<5 and c>a+b): • print ("good" ) • else: • print ("ok“) Q14. What is the output of the following code? (A) good (B) It will produce no output (C) ok (D) It will produce an error

16. Question 6 a>b is True (15>13) d>4 is True (6>4) The rest will not be evaluated good will be printed

17. Question 7 • for i in range(0,10): • print (i) • i = 0 • while(i < 11): • print (i) Q15. Consider the following five loops (i-v). Which loops will generate the same output? (i) (ii)

18. Question 7 • for i in range(10) : • print (i) • for i in range(10%10,10%11) : • print (i) • i = -1 • while(i < 10): • i = i + 1 • print (i) (iii) (iv) (v) (A) i, ii, iii, iv (B) i, ii, iv, v (C) i, iii, iv (D) i, iii, v

19. Question 7 (i) will print 0~9 (ii) will print 0~10 (iii) will print 0~9 (iv) 10%10=0, 10%11=10, will print 0~9 (v) will print 0~10

20. Question 8 • for i in range(1,10,2): • if i % 2 == 0: • print (i) Q17. Considering the following code snippet, what sequence of numbers is printed? (A) All even numbers greater than 0 and less than 10 (B) All odd numbers greater than 0 and less than 10 (C) Every other odd number greater than 0 and less than 10 (D) Nothing

21. Question 8 for i in range(1,10,2): will loop through 1,3,5,7,9 None of them satisfy the condition i%2==0 Nothing will be printed

22. Question 9 • x = 0 • y = 10   • def t1(): • x = 1   • def t2(): • x = 2   • def t3(): • x = y Q19. Considering the following code snippet, what would the output be if you ran the function t4()?

23. Question 9 • def t4(): • x = 4 • t1() • t2() • t3() • print (x) (A) 4 (B) 2 (C) 1 (D) 10 Within each functions, x is just a local variable. Calling t1(), t2(), t3() will not change the local variable x in t4(). (A) is correct. Then how to change a global variable within a function?