Chapter 2 - Control Structures

1
??????? ????? ? ?????- 2

• ???? ???????? 1

2
??? ???? ????? ??????

• ????? ?????
• ??????? ?????? ?? ?????? ?? ????? ??? ???? ????
  ?? ????
• ????? ???? ? ?????? ??
• ????? ????? ?? ???? ?? ????? ????? ????? ?????
  ???? ????
• ??????? ??? ?????? ?? ?? ???? ?? ??????????? ??
  ????
• ??????? ????? if, if-else, switch
• ??????? ??? ? ??????if, if-else, switch
• ??????? ????? ????? while, do/while , for

3
????? ?? ??????? ?? ???????

• ????? ?? ??????? ?? ???????
• ???? ?? ????? ????? ?? ??? ?? ????? ??????? ??
  ????? ???? ????
• ????? ?? ???????? ????? ???? ???
• ????? ????? ????? ??????? ???? ?? ?? ???? ?????
• ????
• ???? ???? 10 ???? ??????? ?????? ???? ???????
  ????? ??? ???? ?? ????? ????

4
????? ?? ??????? ?? ???????

• ???????? ????
• Set total to zero
• Set grade counter to one
• While grade counter is less than or equal to ten
• Input the next grade
• Add the grade into the total
• Add one to the grade counter
• Set the class average to the total divided by
  tenPrint the class average

5
?????? ???? ???

• int total // sum of grades entered by user
• int gradeCounter // number of the grades to be
  entered next
• int grade // grade value entered by user
• int average // average of grades
• // initialization phase
• total 0 // initialize total
• gradeCounter 1 // initialize loop counter
• // processing phase
• while ( gradeCounter lt 10 ) // loop 10 times
• cout ltlt "Enter grade " // prompt for input
• cin gtgt grade // input next grade
• total total grade // add grade to
  total
• gradeCounter gradeCounter 1 //
  increment counter by
• // end while
• // termination phase
• average total / 10 // integer division yields
  integer result
• // display total and average of grades
• cout ltlt "\nTotal of all 10 grades is " ltlt total
  ltlt endl
• cout ltlt "Class average is " ltlt average ltlt endl

6
????? ?? ???? (??????/?????)

• ?????
• ?????? ?? ??????? ?? ??????? ????? ???? ?? ??????
  ???. ????? ????????? ???? ?? ????? ????? ??????
  ???? ??? ?????? ?? ??? ????
• ???? ????? ( ?????)
• ????? ???? ???? ?? ?? ???? ?? ???
• ???? ?? ???? ????? ????? ????? ?? ????
• ????? ???? ???? ???? ?????? ??? ?? ?? ?????? ????
  ???? ?????? ????

7
????? ???? ?? ????? Top-Down Design

• ??? ??? ????? ?? ?? ???? ??? ?? ???? ????
• Determine the class average for the quiz
• ??? ??? ??? ?? ?? ????? ?????? ??????
• Initialize variables
• Input, sum and count the quiz grades
• Calculate and print the class average

8
????? ???? ?? ????? ????????

• ???? ???? ?????? ?? ????? ?? ?? ??? (???) ???
• ????? ?? ????? ???? Initialization
• ?????? ????? ???????? ?????? ????? ?? ????
• ??????
• ?????? ??????? ?? ????? ?????? ??? ? ????? ????
  ??? ???? ????? ?? ????
• ?????
• ????? ????? ?????? ? ??? ?? ???
• ????? ???? ?? ????? ? ????? ??? ?? ??? ??? ?????
• Initialize variables
• ??
• Initialize total to zero
• Initialize counter to zero

9
????? ??? ?? ???

• ?????
• Input, sum and count the quiz grades
• ??
• Input the first grade (possibly the sentinel)
• While the user has not as yet entered the
  sentinel
• Add this grade into the running total
• Add one to the grade counter
• Input the next grade (possibly the sentinel)
• ?????
• Calculate and print the class average
• ??
• If the counter is not equal to zero
• Set the average to the total divided by the
  counter
• Print the average
• Else
• Print No grades were entered

10
???? ????? ?? ????

• cout ltlt "Enter grade or -1 to quit "
• cin gtgt grade
• while ( grade ! -1 )total total grade
• gradeCounter gradeCounter 1 cout ltlt "Enter
  grade or -1 to quit "
• cin gtgt grade
• // end while

11
????????? ?????? ?? ?? ??

• ?????
• ????? ?? ????? ????? ??????????(10 ???) ?? ?????
  ???? ???. ?????? ?? ??????? ?? ??? 8 ??? ?? ?????
  ???? ??? ?????? ????? ????? ?? ?????? ???? ???
  ???. ????? ?? ??? ?? 1 (????) ?? 2( ?????) ?????
  ?? ???
• ?? ???? ??? ??
• ??? ?????? ????? 10 ??? ?? ?????? ?? ??? ?? ??
  ???? ????????? ?? ???? ????
• ?? ???? ?? ?? ??????? ??????? ??? ??? ????
  ????? ????? ????????? ? ????? ???????? ?????
  ???????.
• ????? ???????? 1 ?? 2 ???. ??? 1 ???? ? ??? ??
  ???? 2 ???
• ???? ??? ????? ?????
• Analyze exam results and decide if tuition should
  be raised

12
????????? ?????? ?? ?? ??

• ????? ?????
• Initialize variables
• Input the ten quiz grades and count passes and
  failures
• Print a summary of the exam results and decide
  if tuition should be raised
• ?????
• Initialize variables
• ??
• Initialize passes to zero
• Initialize failures to zero
• Initialize student counter to one

13
????????? ?????? ?? ?? ??

• ?????
• Input the ten quiz grades and count passes and
  failures
• ??
• While student counter is less than or equal to
  tenInput the next exam result
• If the student passed
• Add one to passesElse Add one to failures
• Add one to student counter
• ?????
• Print a summary of the exam results and decide if
  tuition should be raised
• ??
• Print the number of passes
• Print the number of failures
• If more than eight students passed Print Raise
  tuition

14

• 1. Initialize variables
• 2. Input data and count passes/failures

15

• 3. Print results
• Program Output

Enter result (1pass,2fail) 1 Enter result
(1pass,2fail) 1 Enter result (1pass,2fail)
1 Enter result (1pass,2fail) 1 Enter result
(1pass,2fail) 2 Enter result (1pass,2fail)
1 Enter result (1pass,2fail) 1 Enter result
(1pass,2fail) 1 Enter result (1pass,2fail)
1 Enter result (1pass,2fail) 1 Passed 9 Failed
1 Raise tuition
16
???????? ????? ??????

• ?????? ???????c c 3 ?? ?? ???? ?? ???? c
  3 ????
• ?????? ?? ??? ???
• variable variable operator expression
• ?? ?? ???? ?? ???
• variable operator expression
• ??? ????
• d - 4 (d d - 4)
• e 5 (e e 5)
• f / 3 (f f / 3)
• g 9 (g g 9)

17
???????? ?????? ? ????

• ?? ???? ?? ??? c c1 ?? ????? ??????? ???? ?
  ???? ???? c
• ?? ???? ????? ?? ???? c-- ?? ?? ??? c -1
  ???????
• Preincrement
• ????? ??? ?? ????? ???? ?? ???? (c or --c)
• ????? ????? ????? ????? ?? ??? ? ??? ??? ??????
  ??? ??? ?? ????? ?? ????
• Posincrement
• ????? ??? ?? ????? ???? ?? ???? (c or c--)
• ??? ?????? ??? ??? ????? ????? ?? ????? ??? ?????
  ?? ????? ?? ??? ??? ????? ???? ????? c ????? 5
  ????
• ????? cout ltlt c ??? 6 ?? ??? ?? ???. ?????
  ????? c ?????? ????? ? ??? ??? ?? ???.
• ????? cout ltlt c ??? 5 ?? ??? ?? ???. ?????
  ????? c ??? ??? ? ??? ?????? ?? ????.

18
???????? ?????? ? ????

• ??? ????? ?? ?????? ??????? ???? ?????
  Preincrement ? Postincrement??? ?????? ?????
• c
• cout ltlt c
• and
• c
• cout ltlt c

19
??????? ????? ?? ???????

• ??????? ????? ?? ???????
• ????? ??????? ???? ???????
• ????? ????? ?????
• ???? ?? ????? ???? ?? ?? ???? ????? ??????? ?????
  ???
• ??? ?????? ?? ???? ??????? ?? ?? ?? ??? ?????
  ???? ???? ?? ???
• ????
• int counter 1 //initialization
• while (counter lt 10) //repetition condition
• cout ltlt counter ltlt endl
• counter //increment

20
??????? ????? ?? ???????

• ?????
• int counter 1
• ????? counter ?? ????? ?? ???
• ????? ?? ??? ??? ?? integer ???
• ???? ?? ????? ???????? ?? ?? ??? ????? ?????? ??
  ???
• ????? ?????? ?? ?? ????? 1 ???? ?? ???

21
???? ????? for

• ??? ??? ???? ????? for ???? ???
• for ( initialization LoopContinuationTest
  increment )
• statement
• ????
• for( int counter 1 counter lt 10 counter )
• cout ltlt counter ltlt endl
• ????? ?? 1 ?? 10 ?? ??? ?? ???

22
???? ????? for

• ???? for ?? ?? ???? ?? ???? while ?????? ???????
  ???
• initialization
• while ( loopContinuationTest)
• statement
• increment
• ?? ???? ????? ????? ?? ?? ??? ????? ???? ? ???
  ???? ????? ????
• for (int i 0, j 0 j i lt 10 j, i)
• cout ltlt j i ltlt endl

23
???? ????? for - ????

• Program to sum the even numbers from 2 to 100

•  
• Sum is 2550

24
?????? ?????? switch

• ??????? ?? ??? ????? ????? ???? ??? ?? ?????
  ????? ????? ?? ????? ???? ???? ?????

 

25

• 1. Initialize variables
• 2. Input data
• 2.1 Use switch loop to update count

26

• 2.1 Use switch loop to update count
• 3. Print results

27
Enter the letter grades. Enter the EOF
character to end input. a B c C A d f C E Incorrec
t letter grade entered. Enter a new
grade. D A b   Totals for each letter grade are
A 3 B 2 C 3 D 2 F 1

• Program Output

28
???? ????? do/while

• ???? ????? do/while ????? ???? whiles ???
• ??? ????? ?? ????? ???? ? ?? ?? ????? ???? ??
  ????? ?? ???
• ?????? ??????
• do
• statement
• while ( condition )
• ???? (??? ???? ????? ????? counter 1 )
• do
• cout ltlt counter ltlt " "
• while (counter lt 10)
• ??? ???? ????? ?? 1 ?? 10 ?? ??? ?? ???
• ??? ??????? ???? ????? ????? ???? ?? ????

 

29
??????? break

• Break
• ?? ???? ??? ?????? ?????? ???????? ?? ???? ??
  ?????? ?????? ???? ?? ???
• ????? ?????? ?? ????? ??? ?? ???? ?? ??????
  ?????? ????? ?? ????.
• ?? ??? ??? ???? ?????? ?? ??? ????? ??????? ?????
  ??? ?? ????? ??? ?? ????? ???? ???

30
????? continue

• Continue
• ?? ??????? ?? ??? ?????? ????? ????? ???? ????
  ????? ????? ? ????? ???? ?? ???? ?? ???.
• ?? ??? ??? ??? ??? ?????? ???? ?? ??????? ?? ???
  ????? ??????

31
???????? ?????

• (logical AND)
• Returns true if both conditions are true
• (logical OR)
• Returns true if either of its conditions are true
• ! (logical NOT, logical negation)
• ????? ????? ???? ?? ????? ?? ???
• ????? ??? ???. ???? ??? ?? ?????? ??? ?? ???
• ???? ???? ????? ????? ??
• Expression Result
• true false falsetrue false
  true!false true

32
????? ????? ? ??????

• ???? ?????? ?????? ?? ?????? ??? ?? ?? ?? ??? ??
  ??????? ?? ????.
• ??? ?????? ???? ??????? ????? ??? ???? ????
• ?? ?????? ?? ????? ????? ??? ?? ????? ?? ???????
  ??? ? ????? ??????? ???
• ????? ??? ????? false ? ????? ??? ??? ????? true
  ??????? ?? ???
• ????
• if ( payCode 4 )
• cout ltlt "You get a bonus!" ltlt endl
• If was replaced with
• if ( payCode 4 ) cout ltlt "You get a bonus!" ltlt
  endl
• Sets paycode to 4
• 4 is nonzero, so the expression is true and a
  bonus is awarded, regardless of paycode.

33
????? ????? ? ??????

• Lvalues
• ??????? ????? ?? ?? ??? ?? ????? ?????? ???? ??
  ?????
• ????? ???? ???? ????? ???
• ??????? ???? ???? ?? ??? ???? ???x4
• Rvalues
• ??????? ????? ?? ???? ?? ??? ???? ????? ??????
  ???? ??????? ???
• ?????? ???? ???? ?? ??? ???? ??? pi3.1515
• Lvalue ?? ?????? ?? ??? rvalue ??????? ??? ???
  ????? ?? ???? ????

34
?????? ????? ???? ?????

• ??? ????? ????? ???? ????? ?? ????? ?? ??????
  ????? ????????? ????? ???
• ?????? ??? ? ????? ????? ?????? ??? ?????????
  ???? ???
• ????? ?????? ????? ?????????
• ??????? ?????? ??????? ??? ?? ?????? ?? ????
  ????? ? ?? ???? ????? ?????. single-entry,
  single-exit
• ??? ?????? ?????
• ?? ???? ???? ??????? ???? ???? ? ?? ???? ??
  ?????? ???? ?? ?? ?? ?????? ???? ????
• ?? ?????? ?? ?? ?????? ?? ??? ?????? ???? ????
  ???? ??????? ????? ????? ????
• ?? ?????? ?? ?? ?????? ?? ?? ?????? ??????
  ??????? ????
• ?????? 2? 3?? ?? ????? ? ????? ???? ??? ??????
  ??? ????? ???? ?? ?????? ?????? ?? ?? ???? ????
  ??? ????

 
 


35
?????? ????? ???? ?????
36
?????? ????? ???? ?????

• ??? ?????? ?? ?? ?? ???? ?? ?????? ??????? ?????
  ???
• Sequence ?????
• Selection ??????
• if, if/else, or switch
• ?? ??????? ?? ?? ???? ?? ????? if ????? ???? ???
• Repetition ?????
• while, do/while or for
• ?? ??? ????? ????? ?? ???? ?? while ????? ????
  ???.

37
?????

• ?? ??????? ?? ??????? ????? ? ?????? ?????? ??
  ??????? ?? ??? ????? N??? ?????? ??? ? ??? ?? ??
  ?? ???? ??????? ????? ???? ??? ???? ????? ???.
• ???? 100 2255