Transcript Introduction To Computer Program

Chapter Outline
• A Brief History of Programming Language
• Introduction to Programming
– What is a computer program and importance of computer
programming
– Importance of good programs.
– Relationship between compilers, interpreters, assemblers
and programs
– C++ program structure
• Program Development Life Cycle
– Problem solving phases; problem definition, algorithm
design and implementation
– Analysis, design, coding, maintenance
Chapter Outcome
At the end of this class, student should be able to:
• Understand the concept and importance of program and
programming
• Differentiate between compiler, program, interpreter and
assembler
• Apply the steps in program development life cycle.
A Brief History Of Programming
Language
• Programming Language is an artificial and formal language
that has a limited vocabulary consisting of a set of keywords
for making up instructions and a set of precise grammar
rules.
• Example: C, C++, Java, COBOL
A Brief History Of Programming Language
The Language of Computer
• Digital signals are sequences of 0s and 1s
• Machine language: language of a computer
Binary digit (bit) The digit 0 or 1
Binary code
 A sequence of 0s and 1s
Byte
 A sequence of eight bits
A Brief History Of Programming Language
Types of Programming Language
Low-level Language
• Machine Language
• Early computers were programmed in
machine language
• Assembly Language
• Assembly language instruction are
mnemonic (use code, easier to remember)
• Assembler: translates a program written in
assembly language into machine language
High-level Language
• Languages that are machine independent.
• Instructions are quite English-like
• Single instruction can be written to
correspond to many operations at the
machine level.
• Include Basic, FORTRAN, COBOL, Pascal, C++,
C, and Java
• Compiler: translates a program written in a
high-level language machine language
• The equation
BMI = weight (kg) / (height (m) x height (m))
• can be written in C++ as:
BMI = weight/pow(height,2);
A Brief History Of Programming Language
Example of Programming Language machine language:
100100 010001 // Load
BMI = weight/pow(height,2);
100110 010010 // Multiply
100010 010011 // Store
assembler
ASSEMBLY LANGUAGE
•LOAD
•STOR
•MULT
•ADD
•SUB
MACHINE LANGUAGE
•100100
•100010
•100110
•100101
•100011
compiler
High Level Language
•BMI = weight/pow(height,2);
Introduction To Programming
What is Computer?
• A device capable of performing computations and
making logical decisions at speed faster than
human being.
• An electronic machine, operating
under the control of instructions
stored in its own memory
Basic Operation of a Computer
Accepting data from a user
INPUT
Manipulating data
PROCESS
Producing results
OUTPUT
STORAGE
Storing results
** These operations are under the control of instructions
stored in the computer’s memory
Component of a Computer
COMPUTER
HARDWARE
The electric, electronic
and mechanical
equipment that makes up
a computer
SOFTWARE
The series of
instructions that tells the
computer hardware how
to perform tasks
What is a program?
•
•
•
•
A program is a set of instructions that tells the computer how to
solve a problem or perform a task.
A program is like a recipe. It contains a list of ingredients
(variables) and a list of directions (statements) that tell the
computer what to do with the variables.
A computer program is a set of detailed directions telling the
computer exactly what to do, one step at a time.
A program can be as short as one line of code, or as long as
several millions lines of code.
What is a program?
• Computer process data under the
control of sets of instructions called
computer program.
• Computer programs guide the
computer through orderly sets of
actions specified by computer
programmers.
What is a programming?
• A programming is designing and writing a computer program.
• The programmer must decide what the program needs to do,
develop the logic of how to do it, and write instructions for the
computer in a programming language that the computer can
translate into its own language and execute.
The Importance Of Good Program
• Some people consider Computer Programming as an Art which
must follow certain standards in order to promote program
clarity, readability, and comprehension so as to produce programs
that are easier to read, test, debug, modify, and maintain.
• Standards that have been emphasize by most of the
programmers are:
– Names for variables, types and functions.
– Indent style and spacing.
The Importance Of Good Program
• Names for variables, types and functions.
– Choosing an appropriate variable names is seen as the basis
for good style programming
– The following are some rules that can be used when naming
variables, types and functions:
• Function names will start with a lower case letter.
• Example:
double averageMark (double, double);
– Variable names start with a lower case letter and the length
must not be more than 40 characters.
– Constant names can be all capital letters.
– Example: const int MAX_SIZE = 10.
The Importance Of Good Program
• Indent style and spacing.
– In order to improve its readability in programming,
indentation is used to format program source code.
– Adding spaces in between sentence makes your program
much more readable.
– A new level of indentation should be used at every level of
statement nesting in your program.
– The minimum number of spaces at each indentation should
be at least 3, and many programmers use a tab mark (typically
8 spaces).
The Importance Of Good Program
• Indent style and spacing.
if (marks > 50)
{
return PASS;
}
else
{
return FAIL;
}
Style 2
Style 1
– Comparison
if(marks>50{return
PASS;} else
{return FAIL;}
Style 1 is much easier to read because they are indented well,
and logical blocks of code are grouped and displayed together
more clearly.
Relationship Between Compilers,
Interpreters, Assemblers and Program
• All programs have to be translated into machine code before
the computer can actually run them.
• Programs written in high-level languages are translated into
machine language by a compiler or interpreter.
Relationship Between Compilers,
Interpreters, Assemblers and Program
• Interpreters
– a computer program that translates and executes a program
written in a high-level language.
– translates the source program, instruction by instruction,
each time that program is run.
– An interpreter translates program statements one at a time.
– Interpreters are helpful during the debugging stage, but are
slower during execution of the finished program.
Relationship Between Compilers,
Interpreters, Assemblers and Program
• Compilers
– a computer program that translates programs written in a
high-level language into machine code.
– translates each high-level instruction into several machinecode instructions all at once time.
• Compiler runs much faster than an interpreted program.
Relationship Between Compilers,
Interpreters, Assemblers and Program
• Assemblers
– Consists of little more than a table look up routine, where
each word of the source language (assembly language) is
looked up in a table for its numerical equivalent, which is
then output as part of the target language program.
– Assembly language generally gives the programmer precise
and direct access to every capability of the computer
hardware.
C++ Program Structure
• How to write a complete program that consist certain
element:
– Begin the program with comments for documentation
– Include header files, if any are used in the program
– Declare variables and constants, if any
– Write the definition of the function main
Elements Of Computer Program
General form of a C++ Program
// Introductory comments
// file name, programmer, when written or modified
// what program does
#include <iostream.h>
void main()
{
constant declarations ;
variable declarations;
executable statements ;
}
Elements Of Computer Program
Example of C++ program:
#include <iostream.h>  compiler directive/header file
braces
void main( ) main function
{
//display greeting message  comment
cout<<”Welcome to CSC 128 class”;  statement
}
OUTPUT
Welcome to CSC 128 class
Elements Of Computer Program
Comments
Preprocessor directives
Function
Begin block
/*
File Name
Programmer
Matrix No
Topic
Program purpose
Date
*/
:
:
:
:
:
:
bmi.cpp
Alif
2006174538
Exercise 1
This program to calculate bmi for a user.
20 October 2013
#include <iostream.h>
#include <math.h>
void main()
{
double weight, height,bmi;
cout << "Enter weight in kg: ";
cin >> weight;
Function Body
cout << "Enter height in meter: ";
cin >> height;
bmi = weight /pow(height,2);
cout << "The BMI is : "<<bmi<<endl;
End block
}
Example
of C++
program:
Elements Of Computer Program
Comments
• Important part of a program's documentation.
• It is used to explain the purpose of a program.
• Explain the parts of program and keep note regarding changes to
the source code.
• Describe about the reason of the program and understand the
program more clearly.
• Increased the user understanding of the program.
• Store the names of programmers for future reference.
• Used to make program documentation.
Comments
• Can be used in 2 ways:
1.
Using /* */ symbol
• Used for one or more than one line of comments in group
• Example:
/* This is the example of comment in C++
program.This is the second line
*/
Comments
2.
Using // symbol
• Used only for one line
• Example:
//
//
This is example of comments
This is the second line
Preprocessor Directive
• A line of code that begins with the # symbol.
• Are processed by preprocessor (which is usually bundled into the
compiler) before compilation.
• Are not executable code lines but instructions to the compiler.
• Each header file stores functions that are related to a particular
application.
• The directive #include <iostream.h> tells the preprocessor to
include the contents of the file iostream.h, which includes input-output
operations (such as printing to the screen).
Function
Main Function
• Every C++ program contains one or more functions, one of which
must be named main.
• Every C++ program has a main function.
• A function is a block of code that carries out a specific task.
• The word main is followed in the code by a pair of parentheses ( ).
Function
Braces
• Right after these parentheses we can find the body of the main
function enclosed in braces { }.
• What is contained within these braces is what the function does when
it is executed.
• Braces used to mark the beginning and end of blocks of code.
• The open braces ({ ) are place in the beginning of code after the main
functions and close braces ( }) are used to show closing of code.
• The code after the ( }) will not be read/evaluate by compiler
Function
Statement
• A function consists of a sequence of statements that perform
the work of the function.
• It consists of instructions or command which make the program
work.
• Each statement in C++ ends with a semicolon (;).
• There are 3 type of statement :
– Input statement- cin>>statement;
– Output statement-cout<<“statement”;
– Operation statement-mathematical operation
Problem Solving Phases
To be a good programmer, you must be a good
problem solver.
To be a good problem solver, you must understand
a problem in a methodical way, from initial
inspection and definition to final solution.
Problem Solving Phases
Program Development Life Cycle
• Creating new program is called program development
• The process associated with creating successful applications
programs is called the Program Development Life Cycle (PDLC).
• There are 5 steps to Program Development Life Cycle:
Analysis
Design
Implementation/ Coding
Testing/ Debugging
Program
Maintenance
Problem Solving Phases
Phase 1: Analysis
• Done by reviewing the program specifications.
– Eliminate ambiguities in the problem statement.
– Other criteria must be identified especially the data that will
be used as input, process involve and output that will be
produced.
• Indicating what the new system should do.
• In this step, the objectives, outputs, inputs, and processing
requirements are determined.
• The program objectives are the problems that you are trying to
solve.
Problem Solving Phases
Phase 1: Analysis
Example of Problem Solving Exercise
• Write a program to calculate the bmi of a user
Objective :
- To calculate the bmi of a user
Output :
- bmi
Input :
- weight , height
Process :
- Declare  double bmi, weight, height
- Calculate  bmi= weight/pow(height,2)
Problem Solving Phases
Phase 2: Design
• Develop a series of steps with a logical order which, when applied
would produce the output of the problem.
• Good program design is very important in order to make the
development process run smoothly, as well as to make future
revisions easier.
• In program design step, a solution is created using structured
programming techniques such as top-down approach and
algorithm which consist of pseudocode and flowchart.
Problem Solving Phases
Phase 2: Design
Algorithm
Problem Solving Phases
Phase 2: Design
What is Algorithm?
• A step-by-step problem solving process in which a solution is
arrived at a finite amount of time.
• A sequence of a finite number of steps arranged in a specific
logical order which when executed will produce the solution for
that problem.
• An algorithm must satisfy some requirements which are:
– Unambiguousness (clear)
– Generality (unspecific)
– Correctness
– Finiteness (limitation)
Problem Solving Phases
Phase 2: Design
Algorithm
Pseudo code
Flowchart
Problem Solving Phases
Phase 2: Design
Algorithm – Pseudocode
• Is a semiformal, English like language with a limited vocabulary that
can be used to design and describe algorithms.
• Each pseudo code statement includes keywords that describe
operations and some appropriate English like description of
operands.
• Each pseudo code statement should be written on a separate line.
Problem Solving Phases
Phase 2: Design
Algorithm – Pseudocode
• The statements that make up a sequence control structure should
begin with unambiguous words such as compute, set and initialize.
• For the selection control structure use an if-else statement.
• For repetition control structure use the for /while
/do..while statement and indent the loop body.
• All words in a pseudo code statement must be unambiguous and as
easy as possible for nonprogrammers to understand.
Problem Solving Phases
Phase 2: Design
Algorithm – Pseudocode
• Example: (Sequential Control Structure)
– calculate the bmi of a user
BEGIN
DECLARE double bmi, weight, height
READ weight, height
CALCULATE bmi=weight/pow(height,2)
DISPLAY bmi
Problem Solving Phases
Phase 2: Design
Algorithm – Pseudocode
• Example: (Selection Control Structure)
– Identify whether a number is a positive or negative number
BEGIN
DECLARE int num
GET num
IF (num>0)
DISPLAY positive number
ELSE
DISPLAY negative number
END
Problem Solving Phases
Phase 2: Design
Algorithm – Pseudocode
•
Example: (Repetition Control Structure)
• Get three numbers and find the total of the three
numbers
BEGIN
DECLARE int num, n, total
INITIALIZE total=0, n=1
WHILE (n<=3)
GET num;
total=total+num;
n++;
DISPLAY total
END
Problem Solving Phases
Phase 2: Design
Algorithm – Flowchart
• A graphic presentation of the detailed logical sequence of steps
needed to solve programming problems.
• Uses geometric symbols and familiar relational operators to provide
a graphic display of the sequence of steps involved in a program.
• The steps in a flowchart follow each other in the same logical
sequence as their corresponding program statements will follow in a
program.
• Different symbols are used to represent different actions, such as
start/stop, decision, input/output, processing, and looping symbols.
Problem Solving Phases
Phase 2: Design
Algorithm – Flowchart
Symbol
Name
Description
Flowline
To connect symbols and indicate the flow of logic
Terminal
Used to represent the beginning (Start) or the end (End) of
a program
Input/Output
Processing
Decision
Used for input and output operations, such as reading
and printing.
Used for arithmetic and data manipulation operations.
Used for any logic or comparisons operations.
This symbol has one entry and two exit paths.
The path chosen depend on whether the answer to
question is “yes” or “no”
Connector
Used to join different flowlines
Offpage Connector
Used to indicate that the flowchart continues to next
page
Problem Solving Phases
Phase 2: Design
Algorithm – Flow Chart
Example:
Sequential Control Structure
Calculate the bmi of a user
Problem Solving Phases
Phase 2: Design
Algorithm – Flow Chart
Example:
Selection Control Structure
• Identify whether a number is a
positive or negative number
Problem Solving Phases
Phase 2: Design
Algorithm – Flow Chart
Example:
Repetition Control Structure
• Get three numbers and find the
total of the three numbers
Problem Solving Phases
Phase 2: Design
Algorithm – Flow Chart
Example: Function
Calculate the area of a room by using 2 functions: getInput()and calculate()
Problem Solving Phases
Phase 2: Design
Algorithm – Flow Chart
Example: using off page connector
Problem Solving Phases
Phase 3: Implementation/Coding
• The pseudo code or flow diagram will be converted to a
program by using a certain programming language (eg.: BASIC,
Java, C++).
• Coding is the actual process of creating the program in a
programming language.
• The coded program is referred to as source code.
• To be executed, the program is converted by the computer to
object code using a special program (compiler or interpreter)
Problem Solving Phases
Phase 4: Testing/Debugging
• Check and verify for the correctness of the result.
• Debugging is the process of making sure a program is free of
errors, or “bugs.”
• Preliminary debugging begins after the program has been
entered into the computer system.
• The process whereby we will correct the error and run the
program successfully
Problem Solving Phases
Phase 5: Maintenance
• Virtually every program, if it is to last a long time, requires
ongoing maintenance.
• Process of updating software so that it continues to be useful.
• A costly process, but can be used to extend the life of a
program.
Question 1
Write a program to calculate pressure using the formula given.
Analysis
OUTPUT
INPUT
PROCESS
Pseudocode
Begin
Declare double ALL variable
GET/READ Patm , h , p , g
CALCULATE p= Patm + hpg
DISPLAY p
END
Flowchart
Question 1- Answer
Write a program to calculate pressure using the formula given.
Analysis
OUTPUT
INPUT
PROCESS
P
Patm, h,p,g
P = Patm + hpg
Pseudocode
BEGIN
DECLARE double P, Patm , Hpg
GET Patm, Hpg
CALCULATE P = Patm + Hpg
DISPLAY P
END
Flowchart
START
DECLARE
double P, Patm , Hpg
GET Patm, Hpg
CALCULATE P=Patm + Hpg
DISPLAY P
END
Question 2
Write the flowchart for the pseudocode given below:
Answer : Flowchart
START
DECLARE
int side1, side2, area
GET side1, side2
CALCULATE area = side1 * side2
DISPLAY area
END
Question 3
Write pseudocode for the flowchart given below:
Pseudocode : ANSWER
BEGIN
DECLARE char Name[50];
double Hours, Rate, Pay
INPUT Name, Hours, Rate
CALCULATE Pay = Hours * Rate
DISPLAY Name, Pay
END
Question 4
Draw a flowchart based on the pseudocode given below:
BEGIN
DECLARE double b,h ,A
GET b,h
COMPUTE A=b*h
PRINT A,b,h
END
(Hint: A-Area of parallelogram, b-base,h-height)
Formula: A=b*h
Flowchart : Answer
BEGIN
DECLARE double b, h, A
GET b,h
COMPUTE
A=b*h
PRINT A,b,h
END
Question 5
A retail store grants its customers a maximum amount of credit.
Each customer’s available credit is his or her maximum amount
of credit minus the amount of credit used. Write a pseudo code
and flowchart algorithm for a program that asks for a customer’s
maximum amount of credit and amount of credit used. The
program should then display the customer’s available credit.
Answer:
Program Analysis / Specification
OUTPUT
availableCredit
INPUT
creditLimit , creditUsed
PROCESS
Available = limit - used
Question 5 : Answer
A retail store grants its customers a maximum amount of credit. Each
customer’s available credit is his or her maximum amount of credit minus
the amount of credit used. Write a pseudo code and flowchart algorithm for
a program that asks for a customer’s maximum amount of credit and
amount of credit used. The program should then display the customer’s
available credit.
Program Analysis / Specification
OUTPUT
INPUT
PROCESS
balance
maxAmount, amountUsed
balance = maxAmount - amountUsed
Pseudocode
BEGIN
DECLARE double balance, maxAmount, amountUsed
READ maxAmount,amountUsed
CALCULATE balance = maxAmount – amountUsed
DISPLAY balance
END
Flowchart
BEGIN
DECLARE double balance,
maxAmount, amountUsed
READ maxAmount,
amountUsed
CALCULATE
balance = maxAmount - amountUsed
DISPLAY balance
END