CS111: PROGRAMMING LANGUAGE1€¦ · A typical programming task can be divided into two phases:...

CS111: PROGRAMMING

LANGUAGE1

Lecture 2: Algorithmic Problem Solving

Agenda

Problem Solving Techniques

Pseudocode

Algorithm

Flow charts

Examples

Dr. Amal Khalifa, 2014

2

How People Solve Problems

A Problem exists when what we have (Data) is not

the same as what we want (information)

People create a solution (called an Algorithm)

which manipulates Data into Information

People do this quickly and often in a complex

way


3

How Computers Solve Problems

Computers also use Algorithms to solve problems,

and change data into information

Computers can only perform one simple step at a

time

Complex “Human” Algorithms must be broken

down into simple step-by-step instructions BEFORE

they can be translated into computer code


4

What is Programming?


5

Planning or scheduling the performance of a task.

Consciously thinking about each step

Example: Accelerating in a car

1. Move right foot to gas pedal

2. Apply pressure to gas pedal with right foot

3. If speed is too high, apply less pressure.

4. If speed is too low, apply more pressure.

ALGORITHMS AND FLOWCHARTS

A typical programming task can be divided into

two phases:

Problem solving phase

produce an ordered sequence of steps that describe

solution of problem

this sequence of steps is called an algorithm

Implementation phase

implement the program in some programming

language


6

Algorithms

(source : wikipedia) In mathematics, computing, linguistics and related disciplines, an algorithm is a procedure (a finite set of well-defined instructions) for accomplishing some task which, given an initial state, will terminate in a defined end-state.

Algorithm: A step-by-step problem-solving process in which

a solution is arrived at in a finite amount of time


7

Problem Solving

Problem Solving is the ability to understand what

you have, what you want, and creating a set of

instructions to change what you have into what you

want

Good Problem Solving Skills are based on

knowledge, experience and logic

Good Programmers NEVER make assumptions


8

9 Dr. Amal Khalifa, 2014

Problem Solving Approach


10

In the programming environment, the problem-solving process involves the following steps:

1. Analyze the problem and outline the problem and its solution requirements.

2. Design an algorithm to solve the problem.

3. Implement the algorithm in a programming language, such as Java.

4. Verify that the algorithm works.

5. Maintain the program by using and improving it, and modifying it if the problem domain changes.

Problem analysis–coding–execution cycle 11


Expressing the Algorithms

A “Standard” way of describing an algorithm must exist if we expect our solution to be understood by others easily

There are standards in programming:

PSEUDOCODE

FLOWCHARTS


12

Pseudo Code

“Pseudo” means “pretend” or “false”

Pseudo Code is pretend or false computer code;

generic English-like terms that are somewhat like

computer code

Pseudo Code is not as standardized as

flowcharts, and does not facilitate the breaking

down of problems as well as a flowchart does


13

Pseudocode (wikipedia)

Pseudocode (derived from pseudo and code) is

a compact and informal high-level description of

a computer programming algorithm that uses the

structural conventions of programming

languages, but omits detailed subroutines,

variable declarations or language-specific

syntax. The programming language is

augmented with natural language descriptions of

the details, where convenient.


14

design an algorithm to find the perimeter and area of a rectangle

Pseudo Code Example 15


Flowcharts

Graphical representations of algorithms

Tool to translate algorithms into software

A Flowchart uses easy-to-understand symbols to

represent actions on data and the flow of data

Flowcharts aid in breaking down a problem into

simple steps


16

Flowchart Symbols

Oval

Parallelogram

Rectangle

Diamond

Hybrid

Name Symbol Use in Flowchart

Denotes the beginning or end of the program

Denotes an input operation

Denotes an output operation

Denotes a decision (or branch) to be made.

The program should continue along one of

two routes. (e.g. IF/THEN/ELSE)

Denotes a process to be carried out

e.g. addition, subtraction, division etc.

Flow line Denotes the direction of logic flow in the program


17

flowcharting 18


Example

Example 1: Write an algorithm and draw a

flowchart to convert the length in feet to

centimeter.

hint: I feet = 30 cm


19

Pseudocode

Input the length in feet (Lft)

Calculate the length in cm (Lcm) by multiplying LFT

with 30

Print length in cm (LCM)


20

Algorithm

Step 1: Input Lft

Step 2: Lcm Lft x 30

Step 3: Print Lcm

START

Input

Lft

Lcm Lft x 30

Print

Lcm

STOP

Flowchart


21

Example 2

Write an algorithm and draw a flowchart that will

read the two sides of a rectangle and calculate its

area.


22

Example 2

Pseudocode

Input the width (W) and Length (L) of

a rectangle

Calculate the area (A) by multiplying

L with W

Print A

23


Example 2

Algorithm

Step 1: Input W,L

Step 2: A L x W

Step 3: Print A

START

Input

W, L

A L x W

Print

A

STOP


24

Example 3

Write an algorithm and draw a flowchart that will

calculate the roots of a quadratic equation

Hint: the roots are:

x1 = (–b + d)/2a and

x2 = (–b – d)/2a

where, d = sqrt ( )

2 0ax bx c

2 4b ac

Dr. Amal Khalifa, 2014 25

Example 3

Pseudocode:

Input the coefficients (a, b, c) of the quadratic equation

Calculate d

Calculate x1

Calculate x2

Print x1 and x2


26

Algorithm:

Step 1: Input a, b, c

Step 2: d sqrt ( )

Step 3: x1 (–b + d) / (2 x a)

Step 4: x2 (–b – d) / (2 x a)

Step 5: Print x1, x2

Example 3


27

4b b a c

START

Input

a, b, c

d sqrt(b x b – 4 x a x c)

Print

x1 ,x2

STOP

x1 (–b + d) / (2 x a)

X2 (–b – d) / (2 x a)

Text book

[1] chapter 1 (pages 13-16)

That’s all for Today!! 28


CS111: PROGRAMMING LANGUAGE1€¦ · A typical programming task can be divided into two phases:...

Documents

Transcript of CS111: PROGRAMMING LANGUAGE1€¦ · A typical programming task can be divided into two phases:...