上海交通大学：《Computational Thinking and Approach》教学资源（课件讲稿）Lecture05 ITERATION Control Structure

上游充通大 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY Computational Thinking and Approach Lecture 5 Dr.Jialiang LU Jialiang.lu@situ.edu.cn

Computational Thinking and Approach Lecture 5 Dr. Jialiang LU Jialiang.lu@sjtu.edu.cn 1

上游充通大 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY Control Structure ITERATION 2

ITERATION Control Structure 2

@ 上降充通大 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY Out ines 。for:definite Loop while:indefinite loop ·Interactive loop ● Sentinel loop 。File loop 。Nested loop ·Dictionary 3

3 Outlines • for: definite Loop • while: indefinite loop • Interactive loop • Sentinel loop • File loop • Nested loop • Dictionary

上降充通大 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY For Loops:A Quick Review The for statement allows us to iterate through a sequence of values. for in : -for i in range(n): The loop index variable var takes on each successive value in the sequence,and the statements in the body of the loop are executed once for each value. 4

4 For Loops: A Quick Review • The for statement allows us to iterate through a sequence of values. • for in : – for i in range(n): • The loop index variable var takes on each successive value in the sequence, and the statements in the body of the loop are executed once for each value

上游充通大 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY For Loops:A Quick Review ● Suppose we want to write a program that can compute the average of a series of numbers entered by the user. e To make the program general,it should work with any size set of numbers. We don't need to keep track of each number entered,we only need know the running sum and how many numbers have been added. 5

5 For Loops: A Quick Review • Suppose we want to write a program that can compute the average of a series of numbers entered by the user. • To make the program general, it should work with any size set of numbers. • We don‟t need to keep track of each number entered, we only need know the running sum and how many numbers have been added

上游充通大 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY For Loops:A Quick Review We've run into some of these things before! -A series of numbers could be handled by some sort of loop.If there are n numbers,the loop should execute n times. We need a running sum.This will use an accumulator. 6

6 For Loops: A Quick Review • We‟ve run into some of these things before! – A series of numbers could be handled by some sort of loop. If there are n numbers, the loop should execute n times. – We need a running sum. This will use an accumulator

上降充通大 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY For Loops:A Quick Review Input the count of the numbers,n 。Initialize sum to 0 ·Loop n times Input a number,x -Add x to sum Output average as sum/n 7

7 For Loops: A Quick Review • Input the count of the numbers, n • Initialize sum to 0 • Loop n times – Input a number, x – Add x to sum • Output average as sum/n

上游充通大学 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY For Loops:A Quick Review averagel.py 井 A program to average a set of numbers 井 Illustrates counted loop with accumulator def main(): n input ("How many numbers do you have?" sum 0.0 for i in range(n): x input ("Enter a number >" sumsum x print "\nThe average of the numbers is",sum/n Note that sum is initialized to 0.0 so that sum/n returns a float! 8

8 For Loops: A Quick Review # average1.py # A program to average a set of numbers # Illustrates counted loop with accumulator def main(): n = input("How many numbers do you have? ") sum = 0.0 for i in range(n): x = input("Enter a number >> ") sum = sum + x print "\nThe average of the numbers is", sum/n • Note that sum is initialized to 0.0 so that sum/n returns a float!

上游充通大 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY For Loops:A Quick Review How many numbers do you have?5 Enter a number >32 Enter a number >45 Enter a number >34 Enter a number >76 Enter a number >45 The average of the numbers is 46.4 9

9 For Loops: A Quick Review How many numbers do you have? 5 Enter a number >> 32 Enter a number >> 45 Enter a number >> 34 Enter a number >> 76 Enter a number >> 45 The average of the numbers is 46.4

上游充通大学 ParisTech SHANGHAI JIAO TONG UNIVERSITY INSTITUT DES SCIENCES ET TECHNOLOGIES PARIS INSTITUTE OF TECHNOLOGY Remember break and continue? continue for i in[1,2,3,4,5,6,7,8,9,10]: more items in no if i ==5: break yes print i =next item for i in[1,2,3,4,5,6,7,8,9,10]: if i==5: continue break print i 10

Remember break and continue? for i in [1,2,3,4,5,6,7,8,9,10]: if i == 5: break print i for i in [1,2,3,4,5,6,7,8,9,10]: if i == 5: continue print i 10