STRUCTURED PROGRAMMING

1
STRUCTURED PROGRAMMING

• Introduction to C

2
The History of C Language

• Developed by Dennis Ritchie
• at Bell Laboratories 1972
• Developed on UNIX Operating System

3
LANGUAGE LEVEL

• C is an intermediate to high-level language
• High level language - English like
• Low level - machine language
• C also provides control of hardware a facility
  not always available with higher level languages

4
Programming Environment

• C has been a compiled language (each
  statement is translated into machine language)
• 5 Steps of Compilation
• preprocessing
• translating
• optimizing
• assembling
• link editing

5
Strengths of C

• Portability across different systems
• Efficiency of C Code
• Ease of Maintenance
• Control over low-level operations

6
Weakness of C

• Syntax is somewhat irregular
• Operators have context sensitive meanings
• Allows programmer to bypass the type system,
  which can be misused.

7
Identifiers or Names in C

• Letters a, digits 1, and underscores _
• start with a letter or underscore _
• case sensitive A a
• max. 31 characters
• not identical to a keyword (void)
• count, first_char,TRUE, char1
• - 1st_integer, void, last-time

8
The Character Set

• Uppercase alphabetic characters
• lowercase alphabetic characters
• digits
• punctuation
• formatting
• graphic characters
• ASCII

9
Format of C Programs

• Free-Format Language
• start at a column
• no special place
• single or multiple lines of code

10
Whitespace Characters

• Separate identifiers or other elements (tokens)
• space
• line feed
• backspace
• horizontal tap vertical tap
• form feed
• carriage return

11
Token

• The compiler divides a C program into groups of
  characters that belong together
• Each group is a token.
• ( ) -

12
Subprograms or Functions

• A C program is an collection of subprograms
  called functions.
• Function heading/parameters/fct block
• type function_name
• variable declarations
• code

13
Shortest C Program

• Function with the name main required
• void because no value is returned
• void main ( void )

14
Calling a Function

• We will have main() call the function
  does_nothing
• void main ( void )
• does_nothing ()

15
Output in C

• Void main ( void )
• printf ( C by Discovery\n )

16
Output-Special Meaning

• \t the tab character
• \b the backspace character
• \ the double quote character
• \ the single quote character
• \\ the backslash character
• \0 the null character

17
The Structured Approach

• main ( ) is the driver of the program
• Each subfunction must be
• 1. Be defined
• 2. Be declared and
• 3. Be called

18
Input and Output with Variables

• the keyword int is the name for a built-in data
  type used to represent integers
• the following declares a variable of type
• int with the name counter
• int counter
• can be declared inside or outside of a function
  block

19
Input with scanf () keyboard

• Scanf () converts intput from the ASCII
  representation entered at the keyboard to the
  internal representation used by the computer.
• It is similar to the printf ()

20
Arithmetic Operations

• addition and unary plus
• - unary minus and subtraction
• multiplication
• / division
• remainder
• a (a/b) b (ab)

21
Precedence of Arithmetic Operations

• High Precedence
• Unary Operators -
• Multiplicative Operators /
• Additive Operators -
• Assignment Operator

22
Compound Assignment

• The first syntax shortcut is
  compound assignment
• The assignment statement
• a a 4
• can be shortened to
• a 4

23
Increment and Decrement by 1 Operations

• Another shortcut in source code is provided for
  incrementing a variable by one.
• a a 1
• a 1
• a

24
Introduction to Functions and Structured
Programming

• The goals of structured programming include
  writing source code that is modular in nature,
  easily modifiable, robust (handles errors
  gracefully) and readable.
• A modular program is composed of many independent
  subprograms or functions in C.

25
Functions (Subprograms)

• Each subprogram or function in C should be
  designed to do one task
• and should not be too long to be understood
  easily.
• Another programming goal is to write subprograms
  that are tools and can be used with little or no
  modifications in many programs
• Variables and constants declared in it

26
Prepocessor Constants

• Defining constants add to programs readability
  and ease of modification.
• Preprocessor directives
• start with
• include
  include ltstdio.hgt
• reads external file into source file here
• define
  define MAXEMPLOYEES 150

27
Function Parameters

• Using parameters is one method of letting a
  function communicate with the rest of the program
  without depending directly on program variables.
• A function parameter is used to carry information
  from one function to another.

28
ANSI C Function Definition

• int f ( int x )
• The heading will appear before the opening brace
  for the function.
• This informs the compiler that the function f
  takes a single parameter that will be referred to
  by the name x in the body of the function and
  that the parameter type is int.

29
Function Calls

• A function call in C consists of the functions
  name, and a pair of parentheses containing the
  actual parameters.
• A function call can appear anywhere that an
  expression of the corresponding type is allowed.
• main ( ) calls f several times
• f ( ) mathematical function

30
Language Elements Introduced

• Comments
• Control Statements
• Conversion Specifications
• Escape Characters
• Function Definitions
• Function Calls
• Function Declarations

31
Language Elements Introduced

• Identifiers
• Library Functions
• Operators
• Preprocessor Directives
• Types
• Variable Declarations

32
Comments

• / This is a comment. /

33
Control Statements

• return
• Used to impart value to a function and to return
  control from a function to the calling
  environment.

34
Conversion Specifications

• d conversion to or from decimal
• x conversion to or from hexadecimal
• o conversion to or from octal

35
Escape Character

• \
• escapes the usual meaning of the next character

36
Escape CharactersExamples

• \t the tab character
• \c a carriage return
• \b the backspace character
• \ the double quote character string
• \ the single quote character
• \\ the backslash character
• \0 the null character
• \n the newline character

37
Function Definitions

• Functions must have a heading and function block.
• The heading contains the function type, a name
  (identifier), a pair of parentheses, and the
  formal parameters
• The function block would contain the declaration
  of the local variables and the executable code.

38
Function Calls

• Consists of the function name,
• a pair of parentheses
• and a semicolon.
• Any actual parameters appear between the
  parentheses.

39
Function Declarations

• Consist of the function type, the function name,
  and a pair of parentheses containing the number
  and type of each parameter.
• int f( int x ) (ANSI Prototype)

40
Identifiers

• Consist of letters a, A
• underscores _
• numbers 1
• They must not start with a number and must not
  conflict with any keyword.

41
Library Functions

• printf ( control string, parameters)
• Does format output. Takes one additional
  parameter for each conversion specification in
  the control string.
• scanf ( control string, parameters)
• Does formatted input. Takes one additional
  paramter for each conversion specification in the
  the control string.

42
Operators

• assignment
• addition
• - unary minus and subtraction
• multiplication
• / division
• remainder

43
Operators

• , -, , compound assignment
• /,
• increment by 1
• -- decrement by 1

44
Preprocessor Directives

• include
• includes a source file or header file at that
  point in the code
• define
• used to define constants for easy readability and
  maintainability

45
Types

• int
• used to represent an integer value
• void
• indicates that a function will not return a value
  or that a function does not take parameters.

46
Variable Declarations

• Consists of the type name followed by a
  comma-separated list of variables and a
  terminating semicolon.
• int counter