Problem Solving Skills
Spring 2017
Introduction to Information and Communication Technologies
CSD-102
Outline
•
Information Processing Cycles
•
Problem Solving
•
Problem
•
Logic Building
•
Structure theorem
•
Pseudo codes
•
Flowcharts
Information Processing Cycle
•
A computer is a machine that, under a program’s direction and control, perfroms
four basic operations:
•
Input
•
Processing
•
Output
•
Storage
•
A program is a sequence of instructions that tells
the computer how to perform these four operations
in order to accomplish a task.
1
st
Basic Operation : Input
•
When a computer is required to take an input from a particular source,
whether it is a terminal, a disk or any other device, the verbs Read and Get are
used.
•
Example :
•
You are writing an essay in MS word
2
nd
Basic Operation : Output
•
When a computer is required to provide output to a device, the verbs Print,
Write, Output, or Display are used in pseudo code.
•
Usually an output Prompt instruction is required before an input Get
instruction.
•
Example :
•
You are viewing and printing your essay
•
Computer displays / writes the added result of 2 values
3
rd
Basic Operation : Processing
•
Arithmetic Operations:
•
Mathematical calculation, Formula, and for these, a programmer uses either actual mathematical symbols or the words for those symbols.•
Comparison or Logical Operations:
•
A computer can compare two variables and select one or two alternate actions•
Example:X = 5, Y = 7 X > Y OR X < Y Z = X + Y
Z = 5 + 7 Z = 12
4
th
Basic Operation : Storage
•
An information is stored in some location in memory called Variable.
•
3 situations when need to store a value to a variable or memory location:
•
To give data an initial value in pseudo code, the verbs Initialize or Set are used
•
To assign a value as a result of some processing the symbols '=' or ‘ ' are written
•
To keep a variable for later use, the verbs Save or Store are used
•
Example:
•
You are downloading a song in your laptop
•
Z = X + Y or Z X + Y
Problem to Solve
What steps would you propose to solve the following problem?
Problem to Solve
•
Problem:
Hair are dirty
•
Solution:
Wash the hair
•
How:
Wash the hair Algorithm
Algorithm
•
Turn on water tab
•
Wet you hair
•
Apply shampoo
•
Leather
•
Rinse hair
•
Dry off
Steps in Problem Solving (in computer
programming)
•
Computer programming can be divided into two phases:
•
Problem solving phase
•
Make an ordered sequence of steps that solves a problem
•
these sequence of steps is called an algorithm
•
Implementation phase
Steps in Problem Solving
•
First produce a general algorithm (one can use pseudocode)
•
Refine the algorithm successively to get step by step detailed algorithm that
is very close to a computer language.
•
Pseudocode is an artificial and informal language that helps programmers
Pseudocode & Algorithm
•
Example 1: Write an algorithm to determine a student’s final grade and
indicate whether it is passing or failing. The final grade is calculated as the
average of four marks.
Pseudocode
Pseudocode:
•
Input a set of 4 marks
•
Calculate their average by summing and dividing by 4
•
if average is below 50
Print “FAIL”
else
Algorithm
•
Detailed Algorithm
•
Step 1:
Input M1,M2,M3,M4
Step 2: GRADE ← (M1+M2+M3+M4)/4
Step 3: if (GRADE < 50) then
Print “FAIL”
else
Print “PASS”
endif
Characteristics of Algorithm
•
Definite and having Input and Output
•
Well-ordered
•
The steps are in a clear order•
Unambiguous
•
The operations described are understood by a computing agent without further simplification.•
Effectively Computable
•
The computing agent can actually carry out the operation•
Algorithms can be executed by a computing agent which is not necessarily a computer
Rules of Algorithm
•
For Input:
Use keyword “Input” or “Get” followed by a list of variables separated by a single comma.
Example
Input a Input a , b Get a Get a,b•
For Output
:
Use keyword “Output”, “Display” or “Print” followed by a variable name or text. Enclose
“text/message” in inverted commas. Do not enclose variable name in inverted commas.
Example
Good Practice:
Show a message
before to prompt user
for input.
Rules of Algorithm
•
Storage/ Assignment
Use the keyword “Set” in combination with “=” or “:=” OR use keyword “=”, “:=” or “<-”
Example
Set X=8
X=8
Set X:=8
X:= 8
X<- 8
01/03/2017 17Good Practice:
• Number your steps.
• Indicate Start and End
Addition of Two Numbers
•
Input: number1 and number2
•
Output: Sum of number1 and number2
•
Steps:
1.
Start
2.
Input number1 , number2
3.
Sum = number1 + number2
4.
Display Sum
Problem Solving
Structure Theorem
Tools and techniques for solving a problem
01/03/2017 19
What is the Structure theorem
•
It states that it is possible to write any algorithm by using only three basic control
structures.
•
Sequence
•
I have to study classes from grade 1 to grade 8.•
I cannot skip any class in order to reach in grade 8.•
Repetition
•
If I am fail in a grade I have to repeat it until pass.•
Selection
Decision/ Selection
•
Sometimes we need to put certain condition before performing some action, then action will
depend upon the condition if its fulfilled or not Selection statements help us to get this thing
done
•
This construct represents the decision making abilities of the computer to compare two
pieces of information and select one of two alternative actions.
•
In pseudocode, selection is represented by the keywords IF, THEN, ELSE and ENDIF
•
An IF statement always has a condition to check, often a comparison between a variable and a number.•
The IF statement also must specify what to do if the condition/comparison is true.•
These instructions (for “true”) may come after the word THEN, or they may simply be listed.Types of Selection
•
IF – THEN – ENDIF(Single IF)•
Single IF selection statement either performs (selects) an action if a condition is true or skips the action if the condition is false.•
IF – ELSE – ENDIF (Double IF)•
The IF-ELSE selection statement performs an action if a condition is true and performs a different action if the condition is false•
IF – ELSE IF – ELSE – ENDIF (Multiple IF)•
The IF – ELSE IF – ELSE selection statement performs one of many different actions, depending on the value of an expression.•
Switch (Alternate to Multiple IF)Rules for Selection statement
•
One Option IF (condition) then <<steps>> Endif•
Two Options IF(condition) then <<steps>> Else <<steps>> Endif•
Multiple Conditions IF (condition) then <<steps>>Else if(condition) then <<steps>>
Else if (condition) then <<steps>>
Else <<steps>> Endif
Decision/ Selection
Problem: Input the marks of the students and display pass if the marks are 50 else display fail. Start
Step 1: Input Marks
Step 2: IF Marks > 50 THEN
Step 3:
Display “Pass”
Step 4: ELSE
Step 5: Display “Fail” Step 6: ENDIF
Repetition
•
A loop is a repetition of all or part of the commands in a program.
•
A loop often has a counter (a variable) and continues to repeat a specified number of times.
•
A loop may also continue till than a condition is true or until a certain condition is met (e.g.,
until the end of a file or until a number reaches a set limit)
•
Example
•
WHILE condition p is true•
Statement(s) to execute•
ENDWHILETypes of Repetition
•
WHILE
•
while loop is a control flow statement that allows code to be executed repeatedly based on a given boolean condition. The while loop can be thought of as a repeating if statement.•
DO WHILE
•
The DO WHILE statement performs the action (or group of actions) in its body at least once.•
FOR
•
The FOR loop allows code to be repeatedly executed.While Loop
•
The while loop is used to repeat a section of code an unknown number of times until a
specific condition is met.
•
While loops execute blocks of code over and over again.
•
The advantage to a while loop is that it will go (repeat) as often as necessary to accomplish
its goal.
•
Algo rules:
while ( condition ) <<steps>> end while
•
The "something" should eventually result in the condition being false
Example: While Loop
while (condition)action
•
How it works:• if condition is true then execute action
• repeat this process until condition evaluates to false
•
action is either a single statement or a group of statements.•
Examplewhile (number<10)
Display “Hello number ” number “player” Number=Number +1
Do While Loop
•
The DO WHILE statement performs the action (or group of actions) in its body at
least once.
Do
<<steps>>
While (condition)
•
Example
number =1
Do
Display “Hello number ” number “player” Number=Number +1
while (number<10)
For Loop
•
A for loop is classified as an iteration statement.
•
Unlike many other kinds of loops, such as the while loop, the for loop is often
distinguished by an explicit loop counter or loop variable.
•
This allows the body of the for loop to know about the sequencing of each iteration.
•
For loops are also typically used when the number of iterations is known before
entering the loop.
•
For loops are the shorthand way to make loops when the number of iterations is
known, as a for loop can be written as a while loop.
Example
•
RULES
For (initialize; condition; change)
<<steps>>
End for
•
Example
For (number=1; number<10;number++)
Display “Hello number ” number “player”
For Vs. While
•
For loop is used when you know the number of iterations you have to make,
mean when you know how many times to execute a loop.
•
WHILE is used when you are not sure about the iterations but you know what
the condition is and then you can loop that till the condition is met.
Repetition
•
Pretest loop: evaluation occurs before the statements within the loop are processed•
Posttest loop: evaluation occurs after the statements within the loop are processed•
The step at which the loop starts is called its "entrance"•
The last step performed before completion is called its "exit".•
The conditional test that controls the exit from a loop should be placed either immediately following the entrance to the loop or following all steps in its body, but never in the middle of the body.•
Loops with tests at entrance are said to pretest i.e while-do.•
Loops with tests after entire body are said to posttest i.e do-while.•
It is imperative that at least one statement within the statement block alter the condition and eventually render it false, otherwise the logic may result in an endless loop.Repetition
•
Example
Set student_total to 0
WHILE student_total < 10
Read student record
Print student name and address Add 1 to student_total
ENDWHILE
•
The variable student total is initialized before the loop condition is executed. The student
total variable is incremented within the body of the loop so it will eventually stop.
Modules
•
Modules break an algorithm into logical parts (like your groups)
•
Helps with Clarity and Understandability•
Modules can be reused
•
Within the same algorithm•
In a different algorithm•
In Programming Modules can be called:
•
Sub-routines (in older languages)•
Functions (in procedural languages like C/C++)•
Methods (in object oriented languages like Java)Summary
•
In this lecture, we have covered:
•
What is Problem Solving and its Logic Building
•
What is Structure theorem
•
What is algorithm and how to represent it in Pseudo codes and flow chart
Flow Chart
01/03/2017 37
Quick Recap
•
Pseudo-code• High level description of algorithm…
• intended for human reading
• but structured like a programming language
•
Modules (subroutines/ functions/ methods) • Break down bigger algorithms into chunks• Improves Clarity and Reuse
•
Variables• Are named things with a value (like in algebra)
• Can make algorithms more flexible
Pseudo code & Flowchart
•
There are two commonly used tools to help to build logic (algorithm).
•
Pseudo code is an artificial and informal language that helps programmers develop algorithms.•
Pseudo code may be an informal English, combinations of computer languages and spoken language. Whatever works for you.•
A Flowchart is another algorithm but graphical that shows logic solution.•
Emphasizes individual steps and their interconnections.•
A flowchart must have a start and stop.•
A step in a flowchart must connect i.e. You can’t leave a step “hanging” with no connection. e.g. control flows from one action to the next01/03/2017
What is flow chart?
•
The flowchart is one of the most basic methods of representing algorithms. It
is useful as a precise method of explanation in some circumstances.
•
A flowchart is a diagrammatic\pictorial representation of the operations
Flow chart Symbols
•
Start/End
•
Used at the beginning and end of each flowchart.
•
Input/Output
•
Shows when information/data comes into a program or is printed out.
•
Process
•
Used to show calculations, storing of data in variables, and other “processes” that take
place within a program.
Flow chart Symbols
•
Decision
•
Used to show that the program must decide whether something (usually a comparison
between numbers) is true or false. YES and NO (or T/F) branches are usually shown.
•
Connector
•
Used to show that flowchart continues on another page.
•
Flow Direction
•
Show you how you have to move
X>7?
Y
Example
Algorithm
•
Step 1: Input W,L
•
Step 2: A ← L x W
•
Step 3: Print A
START Input W, L A←
L x W STOP Output W, LExample
Input M1,M2,M3,M4
GRADE ← (M1+M2+M3+M4)/4
if (GRADE <50) then
Print “FAIL”
else
Print “PASS”
endif
START Input M1,M2,M3,M4 GRADE←(M1+M2+M3+M4)/4 IS GRADE<5 0 Y N PrintExample
Algorithm
•
Step 1: Input Lft
•
Step 2: Lcm ← Lft x 30
•
Step 3: Print Lcm
Flowchart
START Input Lft Lcm←
Lft x 30 STOP Output LcmTrace Tables & Dry Run
•
Algorithm•
A sequence of steps designed to perform a particular task•
Dry run•
Working through a section of a program manually•
Trace table•
A table constructed with a column to identify the instruction executed and columns for the contents of each variable•
Variable•
The identifier associated with a particular memory location used to store data•
Constant•
A data item with a fixed valueExample 1
•
Algorithm
1.
Start
2.
Set x := 0
3.
input y
4.
x := y * 2
5.
Output x
6.
End
– Trace table
– Let user Input for y s 5
Step Algorithm Lines
X
Y
Output
1
Start
-
-
-2
Set x := 0
0
-
-3
input y
0
5
-4
x := y * 2
10
5
-5
Output x
10
5
10
6
End
-
-
-A - indicates Nil
Example 2
01/03/2017 49
– Algorithm : Take five inputs from user, calculate and display their sum and average
(Without using loop)
1.
Start
2.
input : num1, num2, num3, num4 and num5
3.
Set sum := 0 , average := 0 , totalNumbers :=5
4.
input in num1, num2, num3, num4 and num5
5.
sum := num1 + num2 + num3 + num4 + num5
6.
average := sum / totalNumbers
7.
Print “Sum is ” sum
8.
Print “Average is ” average
9.
End
Example 2
–
Trace table: Take five inputs from user, calculate and display their sum and
average (Without using loop)
– Assume input: 25, 17, 34, 9, 75
# Algorithm Lines num1 num2 num3 num4 num5 sum average totalNu mbers
Output
1 Start - - -
-2 input : num1, num2, num3, num4 and
num5
- - -
-3 Set sum := 0 , average := 0 , totalNumbers :=5
- - - 0 0 5
-4 input num1, num2, num3, num4 and
num5
25 17 34 9 75 0 0 5
-5 sum := num1 + num2 + num3 + num4 +
num5
25 17 34 9 75 0 0 5
-6 average := sum / totalNumbers 25 17 34 9 75 160 32 5
-7 Print “Sum is ” sum 25 17 34 9 75 160 32 5 Sum is 160
8 Print “Average is ” average 25 17 34 9 75 160 32 5 Sum is 160
Example 3
01/03/2017 51
– Algorithm : Take five inputs from user, calculate
and display their sum and average (Without
using loop)
1.
Start
2.
Num=0
3.
Set sum := 0 , average := 0 , totalNumbers :=5
4.
Input num
5.
sum := sum + num
6.
Input num
7.
sum := sum + num
8.
Input num
9.
sum := sum + num
10.
Input num
11.
sum := sum + num
12.
Input num
13.
sum := sum + num
14.
average := sum / totalNumbers
15.
Print “Sum is ” sum
16.
Print “Average is ” average
Example 3
–
Take five inputs from user using only 1 variable for input, calculate and display
their sum and average (Without using loop)
– Assume input: 25, 17, 34, 9, 75
# Algorithm Lines num sum average totalNumbers Output
1 Start - - - -
-2 num=0 0 - - -
-3 Set sum := 0 , average := 0 , totalNumbers :=5 - 0 0 5
-4 Input num 25 0 0 5
-5 sum := sum + num 25 25 0 5
-6 input num 17 25 0 5
-7 sum := sum + num 17 42 0 5
-8 Input num 34 42 0 5
-9 sum := sum + num 34 76 0 5
-Example 3
01/03/2017 53
–
Take five inputs from user using only 1 variable for input, calculate and display
their sum and average (Without using loop)
– Assume input: 25, 17, 34, 9, 75
# Algorithm Lines num sum average totalNumbers Output
12 Input num 75 85 0 5
-13 sum := sum + num 75 160 0 5
-14 average := sum / totalNumbers 75 160 32 5
-15 Print “Sum is ” sum 75 160 32 5 Sum is 160
16 Print “Average is ” average 75 160 32 5 Sum is 160
Average is 32
-Example 4
1. Start
2. Set num1=0, num2=0, num3=0, num4=0, num5=0
3. Set totalSum := 0 , sumOfEven := 0, average := 0 ,
totalNumbers := 5
4. input num1, num2, num3, num4 and num5
5. sum := num1 + num2 + num3 + num4 + num5
6. average := sum / totalNumbers
7. If (num1 mod 2 = 0 )
8. Then sumOfEven := sumOfEven +num1
9. End if
10. If (num2 mod 2 = 0 )
11. Then sumOfEven := sumOfEven +num2
12. End if
13. If (num3 mod 2 = 0 )
14. Then sumOfEven := sumOfEven +num3
15. End if
16. If (num4 mod 2 = 0 )
17. Then sumOfEven := sumOfEven +num4
18. End if
19. If (num5 mod 2 = 0 )
20. Then sumOfEven := sumOfEven +num5
21. End if
22. Print “Total Sum is ” sum
23. Print “Average is ” average
24. Print “Sum of evens is ” sumOfEven
– Algorithm : Take five inputs from user using only 1 variable
for input, calculate and display their totalSum, sumOfEven
and average (Without using loop)
Example 4
01/03/2017 55
– Algorithm : Take five inputs from user using only 1 variable for input, calculate and
display their totalSum, sumOfEven and average (Without using loop)
– Assume input: 24, 19, 34, 18, 75
# Algorithm Lines num1 num2 num3 num4 num5 sum sumOfEve n
average totalNumb ers
1 Start - - -
-2 Set num1=0, num2=0, num3=0, num4=0, num5=0
0 0 0 0 0 - - -
-3 Set sum := 0 , sumOfEven := 0, average := 0 , totalNumbers := 5
- - - 0 0 0 5
4 input in num1, num2, num3, num4 and
num5
24 19 34 18 75 0 0 0 5
5 sum := num1 + num2 + num3 + num4 +
num5
24 19 34 18 75 0 0 0 5
6 average := sum / totalNumbers 24 19 34 18 75 170 0 34 5
7 If (num1 mod 2 = 0 ) 24 19 34 18 75 170 0 34 5
8 Then sumOfEven := sumOfEven +num1 24 19 34 18 75 170 24 34 5
Example 4
01/03/2017 56
– Algorithm : Take five inputs from user using only 1 variable for input, calculate and
display their totalSum, sumOfEven and average (Without using loop)
– Assume input: 24, 19, 34, 18, 75
# Algorithm Lines num1 num2 num3 num4 num5 sum sumOfEve n
average totalNumb ers
10 If (num2 mod 2 = 0 ) 24 19 34 18 75 170 24 34 5
11 Then sumOfEven := sumOfEven
+num2
24 19 34 18 75 170 24 34 5
12 End if 24 19 34 18 75 170 24 34 5
13 If (num3 mod 2 = 0 ) 24 19 34 18 75 170 24 34 5
14 Then sumOfEven := sumOfEven
+num3
24 19 34 18 75 170 58 34 5
15 End if 24 19 34 18 75 170 58 34 5
16 If (num4 mod 2 = 0 ) 24 19 34 18 75 170 58 34 5
17 Then sumOfEven := sumOfEven
+num4
24 19 34 18 75 170 76 34 5
18 End if 24 19 34 18 75 170 76 34 5
19 If (num5 mod 2 = 0 ) 24 19 34 18 75 170 76 34 5
Example 4
01/03/2017 57
– Algorithm : Take five inputs from user using only 1 variable for input, calculate and
display their totalSum, sumOfEven and average (Without using loop)
– Assume input: 24, 19, 34, 18, 75
# Algorithm Lines num1 num2 num3 num4 num5 sum sumOfEve n
average totalNumb ers
22 Print “ Total Sum is ” sum 24 19 34 18 75 170 76 34 5
23 Print “Average is ” average 24 19 34 18 75 170 76 34 5
24 Print “ Sum of evens is ” sum 24 19 34 18 75 170 76 34 5
25 End - - -
-Output
22 Total Sum is 170 23 Total Sum is 170 Average is 34 24 Total Sum is 170 Average is 34 Sum of evens is 76Example 5
–
Algorithm:
1. Start
2. Num=0
3. Set sum := 0 , average := 0 , totalNumbers := 5, loopCounter := 1
4. Repeat while (loopCounter <= totalNumbers)
5. Begin
6. input num
7. display “Enter input ” loop counter “:” 8. sum := sum + num
9. loopCounter = loopCounter + 1
10. End while
11. average := sum / totalNumbers
12. Print “Total Sum is ” sum
Take five inputs from user, calculate and display their
sum and average (With using loop)
Example 5
01/03/2017 59
Take five inputs from user, calculate and display their sum
and average (With using loop)
– Assume input: 25, 17, 34, 9, 75
# Algorithm Step
Loop Pass / Iteration
num sum average totalNumbers loopCounte r loopCounter <= totalNumbers 1 1 - - - -2 2 - 0 - - - - -3 3 - - 0 0 5 1 -4 4 - - 0 0 5 1 True 5 5 1 - 0 0 5 1 True 6 6 1 25 0 0 5 1 True 7 7 1 25 25 0 5 1 True 8 8 1 25 25 0 5 2 True 9 Repeat --- go to step 4 9 4 - 25 25 0 5 2 True 10 5 2 25 25 0 5 2 True
# Algorithm Step
Loop Pass / Iteration
num sum average totalNumbers loopCounte r loopCounter <= totalNumbers 11 6 2 17 25 0 5 2 True 12 7 2 17 42 0 5 2 True 13 8 2 17 42 0 5 3 True 9 Repeat --- go to step 4 14 4 - 17 42 0 5 3 True 15 5 3 17 42 0 5 3 True 16 6 3 34 42 0 5 3 True 17 7 3 34 76 0 5 3 True 18 8 2 34 76 0 5 4 True 9 Repeat --- go to step 4 19 4 - 34 76 0 5 4 True 20 5 4 34 76 0 5 4 True 21 6 4 9 76 0 5 4 True 22 7 4 9 85 0 5 4 True
01/03/2017 61
# Algorithm Step
Loop Pass / Iteration
num sum average totalNumbers loopCounte r loopCounter <= totalNumbers 9 Repeat --- go to step 4 24 4 - 9 85 0 5 5 True 25 5 5 9 85 0 5 5 True 26 6 5 75 85 0 5 5 True 27 7 5 75 160 0 5 5 True 28 8 5 75 160 0 5 6 True 9 Repeat --- go to step 4 29 4 - 75 160 0 5 6 False
Loop ended --- go to step 10
30 10 - 75 160 32 5 6
-31 11 - 75 160 32 5 6
-32 12 - 75 160 32 5 6
-Step
Output for total algorithm
6 Enter input 1: 25 6 Enter input 2: 17 6 Enter input 3: 34 6 Enter input 4: 9 6 Enter input 5: 75 11 Total Sum is 160 12 Total Sum is 160 Average is 32Example 5.1
01/03/2017 63
– Algorithm: (slight modification in condition and loopCounter value)
1. Start 2. num=0
3. Set sum := 0 , average := 0 , totalNumbers := 5, loopCounter := 0 4. Repeat while (loopCounter < totalNumbers)
5. Begin
6. loopCounter = loopCounter + 1 7. input num
8. Display “Enter input ” loop counter “:” 9. sum := sum + num
10. End while
11. average := sum / totalNumbers 12. Print “Total Sum is ” sum
13. Print “Average is ” average 13. End
Take five inputs from user, calculate and display their
sum and average (With using loop)
Example 5
Take five inputs from user, calculate and display their sum
and average (With using loop)
– Assume input: 25, 17, 34, 9, 75
# Algorithm Step
Loop Pass / Iteration
num sum average totalNumbers loopCounte r loopCounter <= totalNumbers 1 1 - - - -2 2 - 0 - - - - -3 3 - - 0 0 5 0 -4 4 - - 0 0 5 0 True 5 5 1 - 0 0 5 0 True 6 6 1 - 0 0 5 1 True 7 7 1 25 0 0 5 1 True 8 8 1 25 25 0 5 1 True 9 Repeat --- go to step 4 9 4 - 25 25 0 5 1 True
01/03/2017 65
# Algorithm Step
Loop Pass / Iteration
num sum average totalNumbers loopCounte r loopCounter <= totalNumbers 11 6 2 25 25 0 5 2 True 12 7 2 17 25 0 5 2 True 13 8 2 17 42 0 5 2 True 9 Repeat --- go to step 4 14 4 - 17 42 0 5 2 True 15 5 3 17 42 0 5 2 True 16 6 3 17 42 0 5 3 True 17 7 3 34 42 0 5 3 True 18 8 2 34 76 0 5 3 True 9 Repeat --- go to step 4 19 4 - 34 76 0 5 3 True 20 5 4 34 76 0 5 3 True 21 6 4 34 76 0 5 4 True 22 7 4 9 76 0 5 4 True 23 8 4 9 85 0 5 4 True
# Algorithm Step
Loop Pass / Iteration
num sum average totalNumbers loopCounte r loopCounter <= totalNumbers 9 Repeat --- go to step 4 24 4 - 9 85 0 5 4 True 25 5 5 9 85 0 5 4 True 26 6 5 9 85 0 5 5 True 27 7 5 75 85 0 5 5 True 28 8 5 75 160 0 5 5 True 9 Repeat --- go to step 4 29 4 - 75 160 0 5 5 False
Loop ended --- go to step 10
30 10 - 75 160 32 5 5
-31 11 - 75 160 32 5 5
-32 12 - 75 160 32 5
-01/03/2017 67
Step
Output for total algorithm
6 Enter input 1: 25 6 Enter input 2: 17 6 Enter input 3: 34 6 Enter input 4: 9 6 Enter input 5: 75 11 Total Sum is 160 12 Total Sum is 160 Average is 32
Same problem can be done using for loop. Increment
statement will work as last line in the loop.
Example 6
01/03/2017 69
– Algorithm:
1.
Start
2.
input num=0
3.
Set sum := 0 , average := 0 , totalNumbers :=
0, loopCounter := 0
4.
Repeat while (true)
5.
Begin
6. loopCounter = loopCounter + 1
7. input num
8. display “Enter input ” loop counter “:”
9. if (num == -1)
10. then break
11. end if
Take as many inputs as user wants using -1 as sentinel
value, calculate and display their sum and average
10.
end if
11.
totalNumbers := totalNumbers +1
12.
sum := sum + num
13.
End while
14.
average := sum / totalNumbers
15.
Print “Total Sum is ” sum
16.
Print “Average is ” average
Example 6: Trace table
Step
Output for total algorithm
Enter input 1: 25 Enter input 2: 17 Enter input 3: 34 Enter input 4: 9 Enter input 5: 75 Enter input 6: -1 Total Sum is 160 Total Sum is 160 Average is 32
Example 7
01/03/2017 71
– Algorithm:
1.
Start
2.
num=0
3.
Set sum := 0 , average := 0 , totalNumbers :=
0, loopCounter := 0
4.
Repeat while (true)
5.
Begin
6. loopCounter = loopCounter + 1
7. input num
8. display “Enter input ” loop counter “:”
9. if (num == -1)
10. then break
11. end if
Take as many inputs as user wants using -1 as sentinel value,
calculate and display sumOfEvens and sumOfOdds
10.
end if
11.
if (num mod 2 = 0)
12.
then sumOfEvens := sumOfEvens +num
13.
else sumOfOdds := sumOfOdds +num
14.
end if
15.
End while
16.
Print “Sum of Evens : ” sumOfEvens
17.
Print “Sum of Odds : ” sumOfOdds
Example 7: Trace table
Ste
p
Output for total algorithm
Enter input 1: 25 Enter input 2: 18 Enter input 3: 34 Enter input 4: 9 Enter input 5: 75 Enter input 6: -1 Sum of Evens : 52 Sum of Evens : 52 Sum of Oddss : 109