1. EECS 110: Lec 10: Definite Loops and User Input Aleksandar Kuzmanovic Northwestern University http://networks.cs.northwestern.edu/EECS110-s15/

2. Loops ! We've seen variables change in-place before: [ x*6 for x in range(8) ] [ 0, 6, 12, 18, 24, 30, 36, 42 ] remember range ?

3. for ! for x in range(8): print('x is', x) print('Phew!') x is assigned each value from this sequence the BODY or BLOCK of the for loop runs with that x Code AFTER the loop will not run until the loop is finished. 1 2 3 4 LOOP back to step 1 for EACH value in the list

4. four on for for x in range(8): print('x is', x) factorial function? sum the list? construct the list?

5. Fact with for def fact( n ): answer = 1 for x in range(n): answer = answer * x return answer

6. Fact with for def fact( n ): answer = 1 for x in range(1,n+1): answer = answer * x return answer

7. Accumulating an answer… def sum( L ): """ returns the sum of L's elements """ sum = 0 for x in L: sum = sum + x return sum Finding the sum of a list: Accumulator! shortcuts? vs. recursion? sum every OTHER element?

8. Shortcut Shortcuts for changing variables: k = 38 k = k + 1 k += 1 #shortcut for k = k + 1

9. Two kinds of for loops Element-based Loops sum = 0 for x in L: sum += x L = [ 42, -10, 4 ] x "selfless"

10. Two kinds of for loops Element-based Loops L = [ 42, -10, 4 ] x i 0 12 Index-based Loops sum = 0 for x in L: sum += x sum = 0 for i in : sum +=

11. Two kinds of for loops Element-based Loops L = [ 42, -10, 4 ] x i 0 12 Index-based Loops sum = 0 for x in L: sum += x sum = 0 for i in range(len(L)) : sum += L[i] L[i]

12. Sum every other element def sum( L ): """ returns the sum of L's elements """ sum = 0 for i in range(len(L)): if ________: sum += L[i] return sum Finding the sum of a list: Accumulator! shortcuts? vs. recursion? sum every OTHER element?

13. Sum every other element def sum( L ): """ returns the sum of L's elements """ sum = 0 for i in range(len(L)): if i%2 == 0: sum += L[i] return sum Finding the sum of a list: Accumulator! shortcuts? vs. recursion? sum every OTHER element?

14. Extreme Looping What does this code do? print('It keeps on’) while True: print('going and') print('Phew! I\'m done!')

15. Extreme Looping Anatomy of a while loop: print('It keeps on') while True: print('going and') print('Phew! I\'m done!’) “while” loop the loop keeps on running as long as this test is True alternative tests? This won't print until the while loop finishes - in this case, never!

16. Extreme Looping import time print('It keeps on') while True: print('going and') time.sleep(1) print('Phew! I\'m done!') “while” loop Slowing things down… the loop keeps on running as long as this test is True

17. Making our escape! import random escape = 0 while escape != 42: print('Help! Let me out!’) escape = random.choice([41,42,43]) print('At last!’) how could we count the number of loops we run?

18. Loops aren't just for lists… for c in 'down with CS!': print(c)

19. "Quiz" What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print(n) def min( L ): Write a loop to find and return the min of a list, L L is a list of numbers. n = 3 while n > 1: print(n) if n%2 == 0: n = n/2 else: n = 3*n + 1 def isPrime( n ): Names: Write a loop so that this function returns True if its input is prime and False otherwise: n is a positive integer

20. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print(n) ?? n = 3 while n > 1: print(n) if n%2 == 0: n = n/2 else: n = 3*n + 1

21. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print n 7 n = 3 while n > 1: print n if n%2 == 0: n = n/2 else: n = 3*n + 1 ??

22. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print n 7 n = 3 while n > 1: print n if n%2 == 0: n = n/2 else: n = 3*n + 1 3

23. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print n 7 n = 3 while n > 1: print n if n%2 == 0: n = n/2 else: n = 3*n + 1 3 10

24. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print n 7 n = 3 while n > 1: print n if n%2 == 0: n = n/2 else: n = 3*n + 1 3 10 5

25. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print n 7 n = 3 while n > 1: print n if n%2 == 0: n = n/2 else: n = 3*n + 1 3 10 5 16

26. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print n 7 n = 3 while n > 1: print n if n%2 == 0: n = n/2 else: n = 3*n + 1 3 10 5 16 8

27. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print n 7 n = 3 while n > 1: print n if n%2 == 0: n = n/2 else: n = 3*n + 1 3 10 5 16 8 4

28. What do these two loops print? n = 0 for c in 'forty-two': if c not in 'aeiou': n += 1 print n 7 n = 3 while n > 1: print n if n%2 == 0: n = n/2 else: n = 3*n + 1 3 10 5 16 8 4 2

29. def min( L ): L is a list of numbers. def isPrime( n ): n is a positive integer

30. L is a list of numbers. def isPrime( n ): n is a positive integer def min( L ): mn = L[0] for i in range(1,len(L)): if L[i] < mn: mn = L[i] return mn

31. L is a list of numbers. def isPrime( n ): n is a positive integer def min( L ): mn = L[0] for i in range(1,len(L)): if L[i] < mn: mn = L[i] return mn def min( L ): mn=L[0] for s in L: if s < mn: mn = s return mn

32. def min( L ): mn = L[0] for i in range(1,len(L)): if L[i] < mn: mn = L[i] return mn def min( L ): mn=L[0] for s in L: if s < mn: mn = s return mn L is a list of numbers. def isPrime( n ): for i in range (n): if i not in [0,1]: if n%i == 0: return False return True n is a positive integer

33. Consider the following update rule for all complex numbers c: z 0 = 0 z n+1 = z n 2 + c If z does not diverge, c is in the M. Set. Real axis Imaginary axis c Lab 8: the Mandelbrot Set Benoit M. z0z0 z1z1 z2z2 z3z3 z4z4

34. Consider the following update rule for all complex numbers c: z 0 = 0 z n+1 = z n 2 + c If c does not diverge, it's in the M. Set. Real axis Imaginary axis c Lab 8: the Mandelbrot Set Benoit M. z0z0 z1z1 z2z2 z3z3 z4z4 example of a non-diverging cycle

35. Consider the following update rule for all complex numbers c: z 0 = 0 z n+1 = z n 2 + c Lab 8: the Mandelbrot Set The shaded area are points that do not diverge.