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### CS 240Computer Programming 1

Flowcharts

Algorithm

An informal definition of an algorithm is:

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

Algorithm

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.

How to understand the problem?

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)

Tools

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

Flowcharts

Pseudo code

Flowchart

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.

Flowchart Rules

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.

1.Simple sequential Flowchart

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

1.Simple sequential Flowchart

Example 3

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

1.Simple sequential Flowchart

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

1.Simple sequential Flowchart

Example 4

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

1.Simple sequential Flowchart

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

1.Simple sequential Flowchart

Example 5

Exercise

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

1.Simple sequential Flowchart

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

2. Branched Flowcharts

Example 1

Construct a flow chart for the following function

F(x) = {

X X>=0

-X X<0

2. Branched Flowcharts

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

2. Branched Flowcharts

Example 2

Trace the following flowchart and write the output of it.

1. When X = 20

2. When X = -10

2. Branched Flowcharts

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

3. Loop Flowcharts

Result

3. Loop Flowcharts

Start

Flowchart

i=0

Sum=0

F

T

While i<10

Read X

avg=Sum/10

Print avg

Sum= X + Sum

Increment i

Stop

Problem: Write Algorithm and Flowchart to find solution of Quadratic equation

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

Problem: Write Algorithm and Flowchart to find solution of Quadratic equation- 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

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