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CS 240 Computer Programming 1

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CS 240Computer Programming 1

Flowcharts

An informal definition of an algorithm is:

a step-by-step method for solving a problem or doing a task.

A step-by-step problem-solving procedure

An algorithm is a sequence of unambiguous instructions for solving a problem.

The number of steps of an algorithm will be countable and finite.

It is a sequence of instructions (or set of instructions) to make a program more readable; a process used to answer a question.

Define the problem

Analyze the problem

Develop an algorithm/method of solution

Write a computer program corresponding to the algorithm

Test and debug the program

Document the program (how it works and how to use it)

There are two commonly used tools to help to document program logic (the algorithm)

Flowcharts

Pseudo code

The production flowchart is a visual representation of the sequence of the program. It shows what comes first, second, third, etc

Definition

A flowchart indicates:

The steps to be taken in order to solve a problem.

The order or the sequence of these steps.

1. Use only one start and one stop per flowchart, --that is, one way in and one way out of the flowchart.

2. The logic flow of the solution is displayed from top to bottom and from left to right.

3. Use the appropriate symbol for each type of operation.

4. Use arrows when moving to another part of the flowchart rather than lines.

5. Do not leave dead-ends--that is, a part of a question unanswered.

Example 1

Construct a flow chart that prints "Hello, World"?

Algorithm

Step 1- Start

Step 2- Print "Hello, World"

Step 3- Stop

Flowchart

Start

“Hello, World”

Stop

Example 2

Construct a flow chart that finds the sum of two numbers.

Algorithm

Variables

Step 1- Start

A: First Number

Step 2- Read A

B: Second Number

Step 3- Read B

C: Sum (A+B)

Step 4- Calculate C = A+B

Step 5- Print C

Step 6- Stop

Start

Flowchart

Read A

Read B

C= A+B

Print C

Stop

Example 3

Construct a flow chart that finds the sum, average and product of three numbers.

Algorithm

Variables

Step 1- Start

X: First Number

Step 2- Read X, Y, Z

Y: Second Number

Step 3- CalculateS = X+Y+Z

Z: Third Number

Step 4- Calculate A = S/3

S: Sum (X+Y+Z)

Step 5- Calculate P = X*Y*Z

A: Average (S/3)

Step 6- Print S, A, P

P: Product (X*Y*Z)

Step 7- Stop

Start

Flowchart

Read X,Y,Z

S= X+Y+Z

A=S/3

P=X*Y*Z

Print S,A,P

Stop

Example 4

Construct a flow chart that finds the difference and the division of two numbers and display the result

Algorithm

Variables

Step 1- Start

N1 : First Number

Step 2- Read N1, N2

N2 : Second Number

Step 3- CalculateD = N1-N2

D: Difference

Step 4- Calculate V = N1/N2

V: Division

Step 5- Print D,V

Step 6- Stop

Start

Flowchart

Read N1, N2

D= N1 –N2

V=N1/N2

Print D,V

Stop

Example 5

Exercise

Construct a flow chart that finds the circle area and circumference of a circle where R (radius) is given

Algorithm

Variables

Step 1- Start

R : Radius

Step 2- Read R

PI: PI = 3.14

Step 3- CalculateA = PI*(R)2

A: Area

Step 4- Calculate C = 2*PI*R

C: Circumference

Step 5- Print R, A, C

Step 6- Stop

Example 1

Construct a flow chart for the following function

F(x) = {

XX>=0

-X X<0

Algorithm

Variables

Step 1- Start

X : Number

Step 2- Read X

F: function of X

Step 3- if X >=0 then F =X

Step 4- if X <0 then F =-X

Step 5- Print F

Step 6- Stop

Start

Flowchart

Read X

YES

NO

X>=0

F=-X

F=X

Print F

Stop

Example 2

Trace the following flowchart and write the output of it.

1. When X = 20

2. When X = -10

Start

Flowchart

>0

0>

Read X

=0

W=SIN(X)+5

X?

W=2*X-1

W=X+1

Print X,W

Stop

Result

When X=-10

When X=20

X= -10

W= -21

X= 20

W= 21

Example 3

Exercise

Draw a flowchart that shows the traffic light processing

Algorithm

Variables

Step 1- Start

C : Traffic light color

Step 2- Read C

Step 3- make a Decision (what is c)

Step 4- if C is RED then Print STOP

Step 5- if C is YELLOW then Print WAIT

Step 6- if C is GREEN then Print PASS

Step 7- Stop

Example 1

Trace the following flowchart and write the output of it.

Start

Flowchart

N=1

Print N

F

T

While N<=7

Stop

N=N+3

Result

Example 2

Trace the following flowchart and write the output of it.

Start

Flowchart

i=0

S=0

F

T

While i<10

Read X

A=S/10

Print A

S= X + S

Increment i

Stop

Start

Flowchart

i=0

Sum=0

F

T

While i<10

Read X

avg=Sum/10

Print avg

Sum= X + Sum

Increment i

Stop

Result

Avg=50/10 =5

START

Read

a, b, c

d sqrt(b x b – 4 x a x c)

x1(–b + d) / (2 x a)

X2 (–b – d) / (2 x a)

STOP

- Algorithm:
- Step 1: Start
- Step 2: Read a, b, c
- Step 3: dsqrt ( )
- Step 4: x1 (–b + d) / (2 x a)
- Step 5: x2 (–b – d) / (2 x a)
- Step 6: Print x1, x2
- Step 7: Stop

Print X1, X2