C++ Flow of Control

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Chapter 1

Introduction to Computers and C++ Programming

Overview

1.1 Computer Systems

1.2 Programming and Problem Solving

1.3 Introduction to C++

1.4 Testing and Debugging

Slide 1- 3

1.1

Computer Systems

 A computer program is…  A set of instructions for a computer to follow

 Computer software is …

 The collection of programs used by a computer  Includes:

 Editors  Translators  System Managers

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Hardware

 Three main classes of computers  PCs (Personal Computer)

 Relatively small used by one person at a time

 Workstation  Larger and more powerful than a PC

 Mainframe  Still larger  Requires support staff  Shared by multiple users

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Networks

 A number of computers connected to share resources  Share printers and other devices  Share information

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Computer Organization

 Five main components  Input devices

 Allows communication to the computer

 Output devices  Allows communication to the user

 Processor (CPU)

 Main memory  Memory locations containing the running program

 Secondary memory  Permanent record of data often on a disk

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Display 1.1

Computer Memory

 Main Memory  Long list of memory locations

 Each contains zeros and ones  Can change during program execution

 Binary Digit or Bit  A digit that can only be zero or one

 Byte  Each memory location has eight bits

 Address  Number that identifies a memory location

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Larger Data Items

 Some data is too large for a single byte  Most integers and real numbers are too large

 Address refers to the first byte

 Next few consecutive bytes can store the

additional bits for larger data

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Display 1.2

Data or Code?

 ‘A’ may look like 01000001  65 may look like 01000001  An instruction may look like 01000001

 How does the computer know the meaning

of 01000001?  Interpretation depends on the current instruction

 Programmers rarely need to be concerned with

this problem.  Reason as if memory locations contain letters and

numbers rather than zeroes and ones

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Secondary Memory

 Main memory stores instructions and data while a program is running.

 Secondary memory  Stores instructions and data between sessions  A file stores data or instructions in

secondary memory

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Secondary Memory Media

 A computer might have any of these types of secondary memory  Hard disk

 Fast  Fixed in the computer and not normally removed

 Floppy disk  Slow  Easily shared with other computers

 Compact disk  Slower than hard disks  Easily shared with other computers  Can be read only or re-writable

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Memory Access

 Random Access  Usually called RAM

 Computer can directly access any memory location

 Sequential Access  Data is generally found by searching through

other items first  More common in secondary memory

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The Processor

 Typically called the CPU  Central Processing Unit  Follows program instructions  Typical capabilities of CPU include:

add subtract multiply divide move data from location to location

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Computer Software

 The operating system  Allows us to communicate with the computer  Is a program  Allocates the computer’s resources  Responds to user requests to run other

programs

 Common operating systems include…  UNIX Linux DOS

Windows Macintosh VMS

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Computer Input

 Computer input consists of  A program

 Some data

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Display 1.3

High-level Languages

 Common programming languages include … C C++ Java Pascal Visual Basic FORTRAN Perl COBOL Lisp Scheme Ada C# Python

 These high – level languages  Resemble human languages  Are designed to be easy to read and write  Use more complicated instructions than

the CPU can follow  Must be translated to zeros and ones for the CPU

to execute a program

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Low-level Languages

 An assembly language command such as ADD X Y Z might mean add the values found at x and y in memory, and store the result in location z.

 Assembly language must be translated to machine language (zeros and ones) 0110 1001 1010 1011

 The CPU can follow machine language

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Compilers

 Translate high-level language to machine language  Source code

 The original program in a high level language  Object code

 The translated version in machine language

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Display 1.4

Linkers

 Some programs we use are already compiled  Their object code is available for us to use  For example: Input and output routines

 A Linker combines

 The object code for the programs we write and

 The object code for the pre-compiled routines into

 The machine language program the CPU can run

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Display 1.5

History Note

 First programmable computer  Designed by Charles Babbage  Began work in 1822  Not completed in Babbage’s life time

 First programmer

 Ada Augusta, Countess of Lovelace  Colleague of Babbage

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Section 1.1 Conclusion

 Can you…  List the five main components of a computer?

 List the data for a program that adds two numbers?

 Describe the work of a compiler?

 Define source code? Define object code?

 Describe the purpose of the operating system?

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1.2

Programming and Problem- Solving

Algorithms

 Algorithm  A sequence of precise instructions that

leads to a solution

 Program  An algorithm expressed in a language the

computer can understand

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Display 1.6

Program Design

 Programming is a creative process  No complete set of rules for creating a program

 Program Design Process

 Problem Solving Phase  Result is an algorithm that solves the problem

 Implementation Phase  Result is the algorithm translated into a

programming language

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Problem Solving Phase

 Be certain the task is completely specified  What is the input?  What information is in the output?  How is the output organized?

 Develop the algorithm before implementation

 Experience shows this saves time in getting your program to run.

 Test the algorithm for correctness

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Implementation Phase

 Translate the algorithm into a programming language  Easier as you gain experience with the language

 Compile the source code

 Locates errors in using the programming language

 Run the program on sample data  Verify correctness of results

 Results may require modification of

the algorithm and program

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Display 1.7

Object Oriented Programming

 Abbreviated OOP

 Used for many modern programs

 Program is viewed as interacting objects  Each object contains algorithms to describe

its behavior  Program design phase involves designing

objects and their algorithms

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OOP Characteristics

 Encapsulation  Information hiding  Objects contain their own data and algorithms

 Inheritance

 Writing reusable code  Objects can inherit characteristics from other objects

 Polymorphism

 A single name can have multiple meanings depending on its context

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Software Life Cycle

 Analysis and specification of the task (problem definition)

 Design of the software (object and algorithm design)

 Implementation (coding)  Maintenance and evolution of the system  Obsolescence

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Section 1.2 Conclusion

 Can you…  Describe the first step to take when creating

a program?

 List the two main phases of the program design process?

 Explain the importance of the problem-solving phase?

 List the steps in the software life cycle?

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1.3

Introduction to C++

 Where did C++ come from?  Derived from the C language  C was derived from the B language  B was derived from the BCPL language

 Why the ‘++’?

 ++ is an operator in C++ and results in a cute pun

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C++ History

 C developed by Dennis Ritchie at AT&T Bell Labs in the 1970s.  Used to maintain UNIX systems  Many commercial applications written in c

 C++ developed by Bjarne Stroustrup at AT&T Bell Labs in the 1980s.  Overcame several shortcomings of C  Incorporated object oriented programming  C remains a subset of C++

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A Sample C++ Program

 A simple C++ program begins this way #include <iostream> using namespace std; int main() {

 And ends this way return 0; }

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Display 1.8

Explanation of code (1/5)

 Variable declaration line int number_of_pods, peas_per_pod, total_peas;

 Identifies names of three variables to name numbers  int means that the variables represent integers

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Explanation of code (2/5)

 Program statement cout << “Press return after entering a number.\n”;  cout (see-out) used for output to the monitor

 “<<“ inserts “Press…a number.\n” in the data

bound for the monitor

 Think of cout as a name for the monitor  “<<“ points to where the data is to end up

 ‘\n’ causes a new line to be started on the monitor

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Explanation of code (3/5)

 Program statement cin >> number_of_pods;

 cin (see-in) used for input from the keyboard

 “>>” extracts data from the keyboard

 Think of cin as a name for the keyboard

 “>>” points from the keyboard to a variable where the data is stored

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Explanation of code (4/5)

 Program statement total_peas = number_of_pods * peas_per_pod;  Performs a computation  ‘*’ is used for multiplication  ‘=‘ causes total_peas to get a new value based on

the calculation shown on the right of the equal sign

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Explanation of code (5/5)

 Program statement cout << number_of_pods;  Sends the value of variable number_of_pods

to the monitor

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Program Layout (1/3)

 Compiler accepts almost any pattern of line

breaks and indentation  Programmers format programs so they

are easy to read  Place opening brace ‘{‘ and closing brace ‘}’

on a line by themselves  Indent statements  Use only one statement per line

Slide 1- 42

Program Layout (2/3)

 Variables are declared before they are used  Typically variables are declared at the beginning of

the program  Statements (not always lines) end with a semi-colon

 Include Directives

#include <iostream>  Tells compiler where to find information about items

used in the program  iostream is a library containing definitions of cin and

cout

Slide 1- 43

Program Layout (3/3)

 using namespace std;  Tells the compiler to use names in iostream in

a “standard” way

 To begin the main function of the program int main()

{  To end the main function

return 0; }  Main function ends with a return statement

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Running a C++ Program

 C++ source code is written with a text editor

 The compiler on your system converts source code to object code.

 The linker combines all the object code into an executable program.

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Run a Program

 Obtain code in Display 1.10  Compile the code  Fix any errors the compiler indicates and

re-compile the code  Run the program  Now you know how to run a program on

your system

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Display 1.10

Section 1.3 Conclusion

 Can you…  Describe the output of this line?

cout << “C++ is easy to understand.”;

 Explain what this line does? cin >> peas_per_pod;

 Explain this? #include <iostream>

Slide 1- 47

1.4

Testing and Debugging

 Bug  A mistake in a program

 Debugging  Eliminating mistakes in programs  Term used when a moth caused a failed relay

on the Harvard Mark 1 computer. Grace Hopper and other programmers taped the moth in logbook stating: “First actual case of a bug being found.”

Slide 1- 49

Program Errors

 Syntax errors  Violation of the grammar rules of the language  Discovered by the compiler

 Error messages may not always show correct location of errors

 Run-time errors  Error conditions detected by the computer at run-time

 Logic errors  Errors in the program’s algorithm  Most difficult to diagnose  Computer does not recognize an error

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Section 1-4 Conclusion

 Can you…  Describe the three kinds of program errors?

 Tell what kind of errors the compiler catches?

 What kind of error is produced if you forget a

punctuation symbol such as a semi-colon?

 Tell what type of error is produced when a program runs but produces incorrect results?

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Chapter 1 -- End

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Slide Number 1
Chapter 1
Overview
1.1
Computer Systems
Hardware
Networks
Computer Organization
Computer Memory
Larger Data Items
Data or Code?
Secondary Memory
Secondary Memory Media
Memory Access
The Processor
Computer Software
Computer Input
High-level Languages
Low-level Languages
Compilers
Linkers
History Note
Section 1.1 Conclusion
1.2
Algorithms
Program Design
Problem Solving Phase
Implementation Phase
Object Oriented Programming
OOP Characteristics
Software Life Cycle
Section 1.2 Conclusion
1.3
Introduction to C++
C++ History
A Sample C++ Program
Explanation of code (1/5)
Explanation of code (2/5)
Explanation of code (3/5)
Explanation of code (4/5)
Explanation of code (5/5)
Program Layout (1/3)
Program Layout (2/3)
Program Layout (3/3)
Running a C++ Program
Run a Program
Section 1.3 Conclusion
1.4
Testing and Debugging
Program Errors
Section 1-4 Conclusion
Chapter 1 -- End
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