CSCI6370: Topics in Computer Science Advanced Topics in Algorithms and Applications Fall Semester, 2002

1
Lecture 5 Layers of Control
2
Nested while Loops

• Problem
• Multiplying two numbers and outputting
• the result only if they are both less
• than 5. (i.e. Start at i1, j1 and go
• from there)
• Formulate pseudocode algorithm
• i 1
• j 1 1 j
• j 2 1 j
• j 3 1 j
• j 4 1 j
• i 2
• j 1 2 j
• j 2 2 j
• j 3 2 j
• j 4 2 j

j 1 While j is less than 5 print out the
result of 1 j j j 1
j 1 While j is less than 5 print out the
result of 2 j j j 1
3
Nested while Loops

• Formulate pseudocode algorithm
• i 3
• j 1 3 j
• j 2 3 j
• j 3 3 j
• j 4 3 j
• i 4
• j 1 4 j
• j 2 4 j
• j 3 4 j
• j 4 4 j

j 1 While j is less than 5 print out the
result of 3 j j j 1
j 1 While j is less than 5 print out the
result of 4 j j j 1
4
Formulate Pseudocode Algorithm

• i 1
• i 2
• i 3
• i 4

j 1 While j is less than 5 print out the
result of 1 j j j 1
i
j 1 While j is less than 5 print out the
result of 2 j j j 1
i 1 While i is less than 5 i i
1
i
j 1 While j is less than 5 print out the
result of 1 j j j 1
i
j 1 While j is less than 5 print out the
result of 3 j j j 1
i
j 1 While j is less than 5 print out the
result of 4 j j j 1
i
5
Pseudocode
i 1 While i is less than 5 i i
1
j 1 While j is less than 5 print out the
result of i j j j 1
6
C Code
7
Nested Control Structures

• Problem
• A college has a list of test results (1 pass,
  2 fail) for 10 students. Write a program that
  analyzes the results as follows
• Input each test result (i.e., a 1 or a 2).
  Display the prompting message Enter result each
  time the program requests another test result.
• Count the number of test results of each type
• Display a summary of the test results indicating
  the number of students who passed and the number
  who failed
• If more than 8 students passed the test, print
  the message Raise tuition.

8
Before Formulate the Algorithm

• The program must process 10 test results
• Counter-controlled loop will be used
• Two counter can be used
• One for number of passes, one for number of fails
• Each test result is a number -- either a 1 or a 2
• If the number is not a 1, we assume that it is a
  2
• Decide if more than 8 students passed the test.

9
Formulate the Pseudocode Algorithm

• Top level outline
• Analyze exam results and decide if tuition should
  be raised
• First refinement
• 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
• Refine Initialize variables to
• Initialize passes to zero
• Initialize failures to zero
• Initialize student counter to one

10
Formulate the Pseudocode Algorithm

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

11
Pseudocode for Test Results Analysis
12
C code for Test Results Analysis
13
C code for Test Results Analysis
14
Assignment Operators

• Assignment operators abbreviate assignment
  expressions
• c c 3
• can be abbreviated as c 3 using the addition
  assignment operator
• Statements of the form
• variable variable operator expression
• can be rewritten as
• variable operator expression
• Examples of other assignment operators
• d - 4 (d d - 4)
• e 5 (e e 5)
• f / 3 (f f / 3)
• g 9 (g g 9)

15
Arithmetic Assignment Operators
16
Increment and Decrement Operators

• Increment operator ()
• Can be used instead of c 1
• Decrement operator (--)
• Can be used instead of c - 1
• Pre-increment/Pre-decrement
• Operator is used before the variable (c or --c)
  
• Variable is changed before the expression it is
  in is evaluated
• Post-increment/Post-decrement
• Operator is used after the variable (c or c--)
• Expression executes before the variable is changed

17
Increment and Decrement Operators

• If c equals 5, then
• printf( "d", c )
• Prints 6
• printf( "d", c )
• Prints 5
• In either case, c now has the value of 6
• When variable not in an expression
• Preincrementing and postincrementing have the
  same effect
• c
• printf( d, c )
• Has the same effect as
• c
• printf( d, c )

18
Increment and Decrement Operators
19
Increment and Decrement Operators
20
Precedence of the Operators
21
In-Class Programming Exercise
Create a program that prints out a triangle with
a user specified width. Example output Enter the
specified width5 X XX XXX XXXX XXXXX XXXX XXX XX
X