The C Language

1
Chapter 1

• The C Language

2
Objectives

• Describe various types of programs
• Describe the role of the operating system
• Describe how a computer gets instructions
• Describe the role of the programming language,
  high- and low-level languages, interpreters, and
  compilers
• Explain the structure of a C program

3
What is a computer program?

• Computers are just machines and must follow
  directions.
• Directions are grouped into logical sequences to
  create programs.
• Programs that perform specific tasks such as word
  processing are called application programs.
• When a computer is first turned on, it must
  follow the instructions embedded in ROM.

4
Operating Systems

• The operating system takes charge of fundamental
  system operations including
• Managing hardware
• Maintaining file systems
• Controlling input and output
• Loading and executing programs

5
The Computers Language

• The microprocessor is the device that actually
  processes the instructions given to the computer.
• Each microprocessor has its own instruction set
  that it can understand.
• The instructions provided to the microprocessor
  must be in machine language.
• Machine language is a combination of circuits
  that can be represented with the binary number
  system.

6
Introduction to Programming Languages

• Programming languages can be understood by people
  and computers.
• Each language has its own set of rules and
  vocabulary.
• Some are very much like English, while others are
  not.

7
Assembly Language

• Uses numbers and letters to represent machine
  language instructions.
• An assembler is needed to change the programmers
  code into machine language.
• Examples of statements might look like the
  following
• PUSH BP
• MOV BP, SP
• MOV SI, 0002

8
Low Level Languages

• It is necessary for the programmer to know the
  instruction set of the microprocessor.
• Programs are specific to a microprocessor.
• Low level programs take up less memory.
• You can do anything that the hardware will allow.

9
High-level Languages

• One command may represent many microprocessor
  instructions.
• You can write programs more quickly.
• Instructions are usually more easy to read.
• Easier to move between computers.

10
Examples of Languages

• High-level
• C
• Java
• Basic
• Pascal
• Visual Basic

• Low-level
• Machine language
• Assembly language

11
Interpreters

• Translate the source code of a high level
  language into machine language code known as
  object code.
• Each instruction is interpreted as it is needed.
• The interpreter must be loaded into memory first.
• Object code is not saved.

12
Compilers

• Also translate high level source into object
  code.
• Makes the translation once and saves an object
  file.
• The object file is combined with other machine
  language by the linker.
• The linker generates the executable file.

13
C Program Structure

• C has some major elements
• Comments
• Compiler directives
• Main function
• Braces
• Statements

14
Comments

• Comments are ignored by the compiler.
• They are used to explain the purpose of the
  program, explain the source code, identify the
  parts of the program or store the names of the
  programmers.
• Comments begin with a double forward slash (//).

15
Compiler Directives

• Instructions to the compiler, not really part of
  the C language.
• A common directive is the include directive
  which inserts other prewritten code into your
  program.
• Includes are usually used to add additional
  functionality such as input/output to your
  program.

16
Main function

• A function is a block of code that carries out a
  specific task.
• Programs are usually divided into many functions,
  but the main function always runs first.
• Functions are typically called from other parts
  of the program and they might return a value.

17
Braces

• Braces are used to mark the beginning and end of
  a block of code.
• Aligning the indention of opening and closing
  braces can make it easier to quickly identify
  blocks of code.

18
Statements

• Statements are instructions that make the program
  work.
• Each statement must end with a semicolon.
• Directives and function declarations do not end
  with semicolons.
• C is case sensitive so capitalization in
  statements does matter.

19
From source code to finished product

• Type source code into text editor.
• Compile the program into object code.
• Link the object code with other machine language
  to generate an executable file.
• The executable file can be run.

20
Summary

• Computers follow instructions called programs.
• Application programs perform specific tasks.
• Operating systems manage fundamental computer
  activities.
• The microprocessor processes each instruction.

21
Summary

• An interpreter or compiler must translate high
  level languages into machine language.
• Experience will teach you what language is
  appropriate for a specific task.
• Comments are ignored by the compiler.
• Directives are commands for the compiler.

22
Summary

• All C programs have a main function. The main
  function is where the program begins running.
• Braces mark the beginning and end of blocks of
  code.
• Statements are the lines of code the computer
  executes.
• Each statement ends with a semicolon.
• C is case sensitive and it ignores extra space.