Transcript Chapter 1 Introduction to Java

Chapter 1 Introduction to
Computers, Programs, and C++
§1.1 Computer and Program
§1.2 Computer Programming
§1.3 Introduction to C++
Computer Is Everywhere
Computer:
-- machine to manipulate data according to instructions.
2
Components of Computers
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
3
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
Memory（内存）
• Memory is to store data and program instructions for
CPU to execute.
• A program and its data must be brought to memory before they
can be executed.
• A memory unit is an ordered sequence of bytes, each
holds eight bits.
• Memory is volatile
• Data is lost when the power is off
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
4
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
How Data Stored?
• Data: numbers, characters, Memory address Memory content
and strings…
.
.
• Computers use “0” and “1” to
.
.
represent all data
.
.
• Encoding and decoding
5
– Data binary code
– automatically done by the computer
2000
01001010
Encoding for character ‘J’
2001
01100001
Encoding for character ‘a’
– The encoding scheme varies.
2002
01110110
Encoding for character ‘v’
• A byte （字节）, of 8 bits
（位）, is the minimum
storage unit
2003
01100001
Encoding for character ‘a’
2004
00000011
Encoding for number 3
Number Systems (数制)
binary
0, 1
octal
0, 1, 2, 3, 4, 5, 6, 7
decimal
0, 1, 2, 3, 4, 5, 6, 7, 8, 9
hexdecimal 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F
6
Computer Program (计算机程序)
• Computer programs
– Known as software, are instructions to the computer.
– You tell a computer what to do through programs.
– Programs are written using programming languages.
Catch the ball!
Come back!
7
§1.2 Computer Programming (编程)
• The process of writing, testing, debugging, and
maintaining the source code of computer
programs
• Programming Procedure
– Problem-solving phase
• Problem analysis and specification
• General solution (algorithm)
• Verification
– Implementation phase
• Concrete solution (program)
• Debugging and test
8
Program vs. Algorithm (算法)
• Program:
– A sequence of instructions written to perform a
specified task with a computer
• Algorithm:
– an effective method expressed as a finite list of
well-defined instructions for calculating a function
Step 1: ….
Step 2: ….
…
9
An Example Algorithm
• Problem:
– The greatest common
divisor/factor of two integers
• Euclid’s algorithm: (1599，650)
10
Pseudo-code (伪代码)
1) Input a and b;
2) If b=0 then a is the answer;
1) Input a, b;
3) Repeat: if a > b then let a = a-b,
2) If b=0 then GOTO 8) ;
otherwise, let b = b-a;
3) If a > b then GOTO 6);
<variable> = <expression>
Until b = 0;
4) Let b=b-a;
IF <condition>
5) The result is a;
5) GOTO DO
2) action;
;
ELSE
6) End.
6) Let a=a-b;
DO next action;
WHILE <condition>
7) GOTO
2);
DO action;
8) Printfora;<variable> from <first value> to <last value> by <step>
DO action with variable;
9) ENDfunction
<function name>(<arguments>)
11
DO action with arguments;
return something;
<function name>(<arguments>) // Function call
Flowchart (流程图)
12
Commonly Used Symbols
• Start and End
• Arrow (flow of control)
• General process
• Input/Output
• Conditional or Decision
13
Programming Language
• An artificial language to express program
• Definition of languages
– Syntax: the surface form
• Lexical structure: regular expressions
• Grammatical structure: Backus–Naur Form
整数
::=
无符号整数 ::=
正负号
::=
数字
::=
[正负号] 无符号整数
数字 { 数字 }
+|0|1|…|9
expression ::= atom | list
atom ::= number | symbol
number ::= [+-]?['0'-'9']+
symbol ::= ['A'-'Z''a'-'z'].*
list ::= '(' expression* ')'
– Semantics: the meaning of statements
14
Language Types/History
High-Level Language
Assembly Language
Machine Language
15
Machine Language （机器语言）
• Machine language is a set of primitive instructions built into
every computer.
• The instructions are in the form of binary code, so you have to
enter binary codes for various instructions.
• Program with native machine language is a tedious process.
• Moreover the programs are highly difficult to read and modify.
• For example, to add two numbers, you might write an
instruction in binary like this:
1101101010011010
16
Assembly Language （汇编语言）
• A symbolic representation of the numeric machine
codes
• assembly code: instruction
• CPU architecture dependent
• Assembler, also a program, is used to convert
programs into machine code.
• For example, to add two numbers:
ADDF3 R1, R2, R3
Assembly Source File
…
ADDF3 R1, R2, R3
…
17
Machine Code File
Assembler
…
1101101010011010
…
High-level Languages（高级语言）
• Languages with natural language elements
• Be easier to use
• Be more portable across platforms.
– hide the details of CPU operations such as memory
access models
• For example:
area = 5 * 5 * 3.1415;
• Compiled vs. interpreted
– BASIC, Perl, …
– C, Java, …
18
Programming Paradigm
• Imperative programming (命令式编程)
Describes computation in terms of statements that change a
program state.
Describing how to go about accomplishing a task.
– Procedural programming
– Object-oriented programming
• Declarative programming (声明式编程)
Describing what the program should accomplish.
– Functional Programming
– Logic programming
–…
19
Compiling vs. Interpreting
(编译语言) (解释语言)
• To “translate” the whole program
AND THEN execute it
– Faster and independent execution
• To interpret the program and execute the
instructions IMMEDIATELY
– Easier to programming
20
Popular Languages
• COBOL: mainly for in business, finance, and administrative systems
for companies and governments
• FORTRAN: mainly for scientific computing
• BASIC: Beginner All-purpose Symbolic Instructional Code
– Visual Basic: Basic-like visual language developed by Microsoft
• Pascal: generic language
– Delphi: Pascal-like visual language developed by Borland
•
•
•
•
•
21
Ada: good for embedded and real-time systems
C: generic language, strong at system programming
C++: an object-oriented language, based on C
Java: C++ like language, Cross-platform (multi-platform)
Script languages: Perl, Python, etc.
§1.3 Introduction to C++
• C, C++, Java, and C# are very similar.
– C++ evolved from C.
– Java was modeled after C++.
– C# is a subset of C++ with some features similar to Java.
• C language  B language  BCPL language
– BCPL was developed by Martin Richards in the mid-1960s for writing operating
systems and compilers.
• C++  C
– Developed by Bjarne Stroustrup at Bell Labs during 1983-1985.
• C++ added a number of features that improved the C
language.
– Most importantly, it added the class.
• An international standard for C++ was created by American
National Standards Institute (ANSI) in 1998.
22
A Simple C++ Program
#include <iostream>
int main()
{
// Display Welcome to C++ to the console
std::cout << "Welcome to C++!" << std::endl;
return 0;
}
23
Extending the Simple C++ Program
#include <iostream>
int main()
{
std::cout << "Welcome to C++!" << std::endl;
std::cout << "Welcome to Visual C++!" << std::endl;
std::cout << "Welcome to C++ Compiler!" << std::endl;
return 0;
}
24
Compiling Source Code
• Source code: a program written in a high-level language
• Compiler: a program used to translate the source
program into an object program, a machine language
program.
• The object program is often then linked with other
supporting library code before execution.
Source File
25
Compiler
Object File
Linker
Excutable File
Procedure of Developing a C++ Program
Create/Modify Source Code
Source code (developed by the programm er)
#in clu de <i os tre am >
int ma in ()
{
/ / D is pla y Wel co me to C+ + to th e c on sol e
s td: :c out < < " We lco me to C ++! " << st d:: en dl ;
r etu rn 0;
}
Saved on the disk
Source Code
Compiler
If com pilation errors
stored on the disk
An obj ect file (e.g., Welcom e.obj ) is created.
Machine Code
program
Linker
stored on the disk
An executable file (e.g., Welcom e.exe) is created.
Executable Code
Run Executable Code
e.g., Welco me
Result
If runtime errors or incorrect result
26
C++ Programming Tools
• Command line tools
– Text editor + compiler
• Visual tools
– C++ builder
– Visual C++
– Visual Studio 2008 etc.
27
Summary
• Basic concepts related to computer
programming
– Computer, program, programming
• Computer programming techniques
– Programming languages
– Programming Paradigms
• Introduction to C++
28