CPSC 217 T03 Week V Part #1: Iteration Hubert (Sathaporn) Hu

Today’s Tutorial Returning A1 TIPS Iteration  While loop  Nested loop  For loop REMINDER: Today is the election day!

Returning A1 There are 2 students who got the bonus mark. They will receive +3 on top of what they already have. I won’t identify the winners here. Please check your assignment.  If you win, you will have “Bonus!” on the assignment.  If I think your work is good, it will have “Bonus candidate” on it.

TIPS 1.You may and should negotiate with me if you think I have made a mistake. However, since we use grade letter for marking, I will not change your mark unless your grade letter will change. 2.Although I encourage you to talk to me about your mark, in my own experience, your mark won’t likely change. 3.Midterm is coming. Be prepared!

Iteration When you want your program to repeat a section of the code, you will need to use iteration. In Python, you can only use 2 kinds of iterations:  While  For

While loop Syntax: while condition: body body will be repeated over and over again until condition becomes false. condition is a Boolean expression. TIP: Be wary of the spacing!

While loop What does this program do? x = 100 while x > 0: print(x, “ bottles. One fell.”)

While loop EXERCISE: Create a program that keeps asking users for a string. The program will only stop when the user enters the correct string. You can make the correct string whatever you want.  For example: Please guess: apple Wrong! Please guess: orange Wrong! Please guess: jackrabbit RIGHT! The program ends!

For loop for and while are logically equivalent. However, for does have a nicer syntax for some occasions. Unlike while, you don’t need to declare the variable used for iteration before hand. What does this program do? for x in range(1, 25): print(x, “ people now in the room.”) EXERCISE: Convert the program to use while.

Nested loop Did you know that you can put a loop in another? It doesn’t matter if you use for or while. You can nest them in any combination you want. You can nest loop in more than 2 levels. Normally, you use nested loops in order to do something multidimensional…  Like filling a multidimensional array.  Like manipulating a table.

Nested loop What does this program do? x = 1 y = 1 while x <= 12: while y <= 12: print (x, “*”, y, “:”, x * y) y += 1 x += 1 y = 0

Nested loop EXERCISE: Try out the exercises on loop given on course website.