COMPSCI 101 Principles of Programming

COMPSCI 101Principles of Programming Lecture 23 – Nested Loops Dr. Patricia J. Riddle

Learning outcomes • At the end of this lecture, students should be able to: • Use nested loops COMPSCI 101 - Principles of Programming

Review of For Loops • For loop • used to access the elements of a list (a sequence of data) • elements are accessed in order • each element is assigned to a variable • a block of instructions is executed after each assignment COMPSCI 101 - Principles of Programming

Nested Loops my_list = [ [ 1 , 2 , 3 ] , [ 4 , 5 , 6 ] , [ 7 , 8 , 9 ] ] for i in my_list: for j in i: print(j) my_words = ["one" , "two" , "three"] for word in my_words: for letter in word: print(letter) COMPSCI 101 - Principles of Programming

Exercise • Write a function named change_case2()that accepts a sentence and returns the same sentence in all uppercase or all lowercase, using nested loops. >>> change_case2("pApEr","upper") 'PAPER' >>> change_case2("PapeR","lower") 'paper' >>> change_case2("Can we dO a WHoleSentence","upper") 'CAN WE DO A WHOLE SENTENCE' COMPSCI 101 - Principles of Programming

Answer COMPSCI 101 - Principles of Programming

Exercise • Write a functionnamed isogram2()that uses nested loops and accepts a word as a parameter and returns True if it is an isogram and False otherwise. • An isogram, sometimes known as a nonpattern word, is a word or phrase in which every letter occurs the same number of times. >>> isogram2("subdermatoglyphic") True >>> isogram2("deed") True >>> isogram2("sara") False COMPSCI 101 - Principles of Programming

Exercise • Write a function named find_primes()that accepts a number as a parameter and returns a list of all the primes up to (and including) that number A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. Wikipedia >>> find_primes(4) [2, 3] >>> find_primes(7) [2, 3, 5, 7] COMPSCI 101 - Principles of Programming

Exercise • Write a function named mutate() that accepts the filename of a file containing a small dictionary, and a word as parameters and returns a list of words which differ from the word by only 1 letter. >>> mutate("dict5.txt","cat") ['bat', 'eat', 'fat', 'hat', 'kat', 'lat', 'mat', 'oat', 'pat', 'qat', 'rat', 'sat', 'tat', 'vat', 'cit', 'cot', 'crt', 'cut', 'cab', 'cad', 'cam', 'can', 'cap', 'car', 'caw', 'cay'] >>> mutate("dict5.txt","frog") ['grog', 'prog', 'flog', 'froe', 'from', 'frow'] COMPSCI 101 - Principles of Programming

Exercise • Write a function named three_letter_anagram()that accepts a word and returns all anagrams of it. >>> three_letter_anagram("cat") ['tac', 'tca', 'atc', 'act', 'cta', 'cat'] >>> three_letter_anagram("men") ['nem', 'nme', 'enm', 'emn', 'mne', 'men'] >>> three_letter_anagram("see") ['ees', 'ese', 'ees', 'ese', 'see', 'see'] COMPSCI 101 - Principles of Programming

Summary • Nested Loops • Can put a loop inside another loop • Just like you can put a conditional inside a loop COMPSCI 101 - Principles of Programming

Tomorrow • Random Number Generation, • User Input, • While Loops COMPSCI 101 - Principles of Programming

COMPSCI 101 Principles of Programming