Lecture Date: Wednesday, September 21
Often there is code that we want our programs to repeat. This could be to have the program process all the items in a list, or do a number of tasks in order, or any number of other reasons. Along with
if statements, loops are a core decision and control structure to write effective programs.
There are several ways to write loops in Python. We'll discuss those all today.
whileloop - a condition-controlled loop
forloop using the
rangeoperator- a count-controlled loop
forloop using the
inoperator with a list
whileloops for input validation
- nested loops
Here are some things we might try to build:
- a shopping cart
- the worst roman.py solution ever
- average of a list of numbers
- printing a square
Some code we did today in class:
num = int(input("number? ")) roman = "" while num > 0: roman += "I" num -= 1 print(roman) x = 10 while x > 5: print(x) x -= 1 word = "" while not word == "stop": word = input("Give me a word (stop to stop): ") print("You said: " + word) ask for number between 1 and 100 (inclusive) if not in range, ask for another if in range, print number = -1 while number < 1 or number > 100: number = int(input("Give me a number between 1 and 100: ")) print(number) number = -1 while number not in range(1,101): number = int(input("Give me a number between 1 and 100: ")) print(number) for i in range(0,4): # [0,1,2,3] print(i) students = ['Mark', 'Colin', 'Sammy', 'Sarah', 'Laurie'] for student in students: print(student) for i in range(100,21,-5): print(i) square = [[1,2,3],[4,5,6],[7,8,9]] # print this: # 1 2 3 # 4 5 6 # 7 8 9 row_to_print = "" for row in square: for col in row: row_to_print += str(col) + "\t" print(row_to_print) row_to_print = ""