PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else...

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PROBLEM SOLVING WITH DECISIONS Chapter 6

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Transcript of PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else...

Page 1: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

PROBLEM SOLVING WITH DECISIONS

Chapter 6

Page 2: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

The decision logic structure

Uses the If/Then/Else instruction . It tells the computer that If a condition is

true , then execute a set of instructions, or Else execute another set of instructions.

The else part is optional As there is not always a set of instruction

if the condition are false .

Page 3: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Common Forms of decision structure

•If <condition (s)>•Then

•<True instructions>•Else

•<False instructions>

T

F

A condition can be one of four things :•Logical expression: (AND, OR NOT)• relational expression(>, <=, <, >=,…..)•Variable logic data type.•Combination of Relational , logic and mathematical operators.•Note: the condition part can combine more than one condition using the logical operators.

Page 4: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Examples.

A < B ( a, b the same data type numeric or character )

X + 5 > = Z ( X , Z are numeric ) E < 5 OR F < 10 DataOk ( is logical datum )

Page 5: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

The decision logic structure

Single condition : A simple decision with only one condition and

one action or set of actions . Multiple condition :

Decisions in which you have multiple conditions that lead to one action or set of actions .

You will use logical operators to connect the conditions .

Page 6: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Single condition one possible action or set of

action write an algorithm and corresponding

flowchart that read a student grade on a test which is out of 10, then alerts the student if his grade is under 4.

Page 7: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Algorithm Flowchart

StudentAlert()1.Integer grade2.Enter grade3.If grade < 4

1. Print “Alert: You must study hard”

4.end

StudentAlert()

Integer grade

Enter grade

If grade < 4

Print “Alert: You must study hard”

End

TF

Page 8: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Single Condition one Possible Actions or Sets of Actions

assume you are calculating pay at an hourly rate , and overtime pay ( over 40 hours ) at 1.5 times the hourly rate .

Page 9: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Single Condition Two Possible Actions or Sets of Actions

Page 10: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

The Multiple If/Then/Else

Three type of decision logic used to for solution consisting for more than one decision: Straight-through Logic Positive Logic Negative Logic

Page 11: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

The Multiple If/Then/Else

1. Straight-through logic : All of the decisions are processed

sequentially , one after the other.

2. positive logic : Not all of the instruction are processed the flow of the processing continues through

the module when the resultant of a decisions is true.

If the resultant is false another decision is processed until the resultant is true or there is no decision to be processed .

Page 12: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

The Multiple If/Then/Else

3. negative logic : the flow of the processing continues

through the module when the resultant of a decisions is false .

when the resultant is true , another decision is processed until the resultant is false or there is no decision to be processed .

Page 13: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

The Nested Decision

In algorithms containing multiple decisions, you may write nested If/Then/Else instructions.

Decisions using positive and negative logic use nested If/Then/Else instructions.

Decisions using straight-through logic do not. Nested If/Then/Else instructions in which

each level of a decision is embedded in a level before it.

Use the nested If/then/Else when one of several possible actions or set of action are to be processed .

Page 14: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Nested If/Then/Else Instructions

Page 15: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

1.Straight-through All decisions (Conditions) are processed

sequentially, one after another. There is no else part of the instructions .

is required when all the decisions have to be processed , and thy are independent of each other .

The false branch always goes to the next decision.

The true branch goes to the next decision after the instruction for the true have been processed .

Least efficient, why? Because all the decisions must be processed .

Page 16: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

1 -Straight-Through Logic Example 1 Write an algorithm to change the value of X to 0 when

X becomes greater then 100, and to change the value of Y to 0 when Y becomes greater then 250.

X > 100 X=0

Y > 250 Y=0

Page 17: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Straight-Through Logic – Example 2

Page 18: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

1 -Straight-Through Logic Example 2

Write an algorithm to find the amount to charge people of varying ages for a concert ticket. When a person is under 16, the charge is $7; when the person is 65 or over, the charge is $5; all others are charged $10.

AgeAge ChargeCharge

Age < 16 7

Age >= 16 AND Age < 65 10

Age >= 65 5

Page 19: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Straight-Through Logic

Page 20: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

2 .Positive Logic The easiest type to use. Why??!!

It is way we think Positive logic works in the following

manner: If the condition is true

the computer follows a set of instructions & continues processing.

If the condition is false the computer process another decision until the

resultant is true, or there are no more decisions to process.

Page 21: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

2 .Positive Logic Example 1

Write an algorithm and corresponding flowchart to find the amount to charge people of varying ages for a concert ticket. When a person is under 16, the charge is $7; when the person is 65 or over, the charge is $5; all others are charged $10.

AgeAge ChargeCharge

Age < 16 7

Age >= 16 AND Age < 65 10

Age >= 65 5

Page 22: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Positive Logic – Example 1

Page 23: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Design an algorithm that Calculate the commission rate of a sales person, given the amount of sales. When the salesperson has sold less than or equal to $2000, the commission is 2%. When the sales total is more than $2000, and less than or equal to $4000, the commission is 4%. When the sales total is more than $4000, and less than or equal to $6000, the commission is 7%. When the person has sold more than $6000, the commission is 10%.

2 .Positive Logic Example 2

SALESSALES CommissionCommission

≤ 2000 .02

2001 - 4000 .04

4001 – 6000 .07

> 6000 .10

Page 24: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Positive Logic – Example 2

Page 25: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

The Conditions in example-2 Set Up in a Different Way

Page 26: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

3 .Negative Logic

Negative logic works in the following manner: If the condition is true

The computer process another decision until the resultant is false, or there are no more decisions to process.

If the condition is false The computer follows a set of instructions & continues

processing.

It is often advantageous to use negative logic to decrease the number of tests or to improve the readability of a program .

Page 27: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

3 .Negative Logic Example 1

Write an algorithm and corresponding flowchart to find the amount to charge people of varying ages for a concert ticket. When a person is under 16, the charge is $7; when the person is 65 or over, the charge is $5; all others are charged $10.

AgeAge ChargeCharge

Age < 16 7

Age >= 16 AND Age < 65 10

Age >= 65 5

Page 28: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Negative Logic – Example 1

age =˃ 16

age =˃ 65

age =˃ 65

age =˃ 16

Page 29: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Design an algorithm that Calculate the commission rate of a sales person, given the amount of sales. When the salesperson has sold less than or equal to $2000, the commission is 2%. When the sales total is more than $2000, and less than or equal to $4000, the commission is 4%. When the sales total is more than $4000, and less than or equal to $6000, the commission is 7%. When the person has sold more than $6000, the commission is 10%.

2 .Negative Logic Example 2

SALESSALES CommissionCommission

≤ 2000 .02

2001 - 4000 .04

4001 – 6000 .07

> 6000 .10

Page 30: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Negative Logic – Example 2

Page 31: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

The Conditions in example-2 Set Up in a Different Way

Page 32: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Logic Conversion

If there are no instruction for the true section of decision instruction , Then it is better to convert the logic type : Change all < to >= Change all <= to > Change all > to <= Change all >= to < Change all = to <> Change all <> to = Interchange all of the Then set of instructions

with the corresponding Else set of instructions.

Page 33: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.
Page 34: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Conversion from Positive Logic to Negative Logic

Page 35: PROBLEM SOLVING WITH DECISIONS Chapter 6. The decision logic structure Uses the If/Then/Else instruction. It tells the computer that If a condition.

Conversion from Positive Logic to Negative Logic


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