Program Construction in C

1
Program Construction in C

• Reading Chapter 2

2
Hello World

• // A first program to display Hello world
• include ltiostreamgt // preprocessor directive
• using namespace std
• int main() // Beginning of function body
• cout ltlt "Hello World!" ltlt endl
• return 0
• Output
• Hello World!

3
Structure of a C program

• A C program is a collection of one or more
  functions.
• There must be a function called main().
• Program execution always begins with the first
  statement in function main().
• Any other functions in the program are not
  executed until they are called.

4
Example

• include ltiostreamgt // preprocessor directive
• using namespace std
• define PI 3.14 // preprocessor directive
• int main() // Function heading
• // Beginning of function body
• int radius // Variable declarations
• float area
• radius 5 // Assignment statements
• area PI radius radius
• cout ltlt "The radius is " ltlt radius ltlt endl
• cout ltlt "The area is " ltlt area ltlt endl
• return 0
• // End of function body

5
Example (Cont..)

• Output
• The radius is 5
• The area is 78.5

6
Basic elements of a C program

• Whitespaces
• Directives
• Comments
• Word Symbols
• Special Symbols
• Variables/Constants
• Statements
• Functions

7
Whitespaces

• Whitespaces are spaces, tabs, line endings, and
  blank lines
• Irrelevant to the compiler
• Should be used in specific places to make your
  program more readable

8
Directives

• Directives tell the preprocessor to do things
• Always begin with
• End at the end of the source line
• The include directive instructs the preprocessor
  to insert the contents of a particular header
  file
• include ltiostreamgt
• include ltstringgt
• The define directive is used to define constants
• define PI 3.14
• define MAX_GRADE 100

9
Comments

• Preceded by //
• Has to be ended in the same line
• C style allows comments to be written between /
  and /
• Can extend over multiple lines
• Ignored by the compiler
• Very important to make a program understandable

10
Word Symbols

• Also called reserved words or keywords
• Part of the C language
• Appendix A (p. 1443) in textbook

11
Special Symbols

• Mathematical symbols
• - /
• Grammar symbols
• . ? ,
• Symbols made from 2 characters
• lt ! gt ?

12
Identifiers

• An identifier is the name used for a data object
  (variable/constant) or for a function.
• The identifiers are case sensitive.
• Using meaningful identifiers is a good practice.

13
Variables/Constants

• Variables
• Used to contain values that can be changed during
  the program execution
• Constants
• Used to contain values that can not be changed
  during the program execution

14
Functions

• A function is a program module that performs some
  particular task.
• A function has a name that can be used to
  reference (or call) the function.
• The function name is preceded by the return type.
• The function name is followed by the argument
  list in parentheses (sometimes there will be no
  arguments and so the parentheses will be empty).

15
Statements

• A statement is an instruction that performs a
  specific operation.
• radius 5
• Every single statement ends with a semicolon ()
  and may extend over multiple lines.
• Where the line ends is usually not important
• However, line breaks are not allowed inside of
  quotations