The C Language

1
Chapter 2

• The C Language

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Hello World

• / A first program to display Hello world /
• include ltstdio.hgt / Compiler directive /
• void main(void) / Beginning of function
  definition /
• printf("Hello World!\n") / Displays on
  screen /
• Output
• Hello World!

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Example

• / Another simple C program /
• include ltstdio.hgt / Compiler directive /
• define MAX_GRADE 20
• void main(void) / Beginning of function
  definition /
• int quiz / Declaration of a
  variable /
• quiz MAX_GRADE / Assignment
  statement /
• / Displays on screen /
• printf("A perfect quiz is i points.\n",
  quiz)
• printf("Will I get perfect scores?\n")

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Example Output

• Output
• A perfect quiz is 20 points.
• Will I get perfect scores?

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General Format
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Parts of a C Program

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

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Whitespace

• spaces, tabs, line endings, and blank lines
• irrelevant to the compiler
• should be used in specific places to make your
  program more readable

8
Outline Form

• Your program should resemble an outline with main
  topics to the left and subordinate topics to the
  right

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Comments

• Comments in C are shown by / and /
• Everything between / and / is ignored by the
  compiler
• Comments are very important to the
  understandability of a program
• Make sure you end all of your comments

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Directives

• Directives tell the preprocessor to do things
• Directives always begin with
• Directives end at the end of the source line
• The include in the example program tells the
  preprocessor to insert the code found in the
  stdio.h file at that location
• The define in the example program names a
  constant

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Word Symbols

• Also called reserved words or keywords
• Part of the C language
• Appendix A (p. 786) in textbook

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Special Symbols

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

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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.

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Statements

• A statement is an instruction that performs a
  specific operation
• quiz 20
• Every single statement ends with a semicolon
• Where the line ends is usually not important
• However, line breaks are not allowed inside of
  quotations
• printf(A perfect quiz is i points.\n,
  quiz)

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Functions

• A function is a set of instructions that performs
  an operation
• A function will always have a name that can be
  used to reference (or call) the function
• The function name will be followed by the
  argument list in parentheses (sometimes there
  will be no arguments and so the parentheses will
  be empty)

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Examination of printf()
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Class Assignment 1

• Write a short program that will print your full
  name to the screen.

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Values in C

• Numeric values
• Real numbers
• Integral numbers (or whole numbers)
• Character values
• ASCII code is an integer value for characters
• The character A is the same as 65 in ASCII

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Special ASCII Characters

• Special characters have a backslash (\) followed
  by a printable character

\0 Null \a Audible alarm \b Backspace \n New
line \r Carriage Return
\t Horizontal tab \v Vertical tab \
Apostrophe \ Quote \? Question
mark \\ Backslash
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Variables

• Represent a location or locations in memory
• Values are placed there to be used in a program
• Values can change, thus are variable
• Variable names are used to reference

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Variable Declarations

• All variables must be declared before being used
• datatype variable initialization
• int frequency
• int startValue 14
• A declaration does a number of things
• Tells the compiler how to store the value
• Defines it, memory is allocated for it
• May initialize it, giving it an initial value

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Data Types

• Data Types
• Basic (Built-In) Data Types
• Derived Data Types
• User Defined Data Types
• Basic (Built-In) Data Types
• Integer types
• Floating point types
• Character type

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Integer Data Types

• Three types based on the size, the size can be
  system specific
• int 32 bits (Microsoft C)
• short int 16 bits (Microsoft C)
• long int 32 bits (Microsoft C)
• Each can be
• signed (default)
• unsigned

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Integer Data Types (Cont ..)

• signed allows the value to be negative
• unsigned allows only positive (and zero)
• The range is approximately double on the positive
  side

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Summary of Integers in Microsoft C
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Floating Point Data Types

• Stored in scientific notation
• Example
• 0.0235 2.35 10?2
• Expressed in standard or scientific notation
• Can use 7146.0 or 7.146e3

Mantissa
Base
Exponent
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Floating Point Types (Cont ..)

• Three flavors
• float 32 bits
• double 64 bits
• long double 80 bits
• Some valid declarations
• float wageRate 12.75
• double area, volume
• long double humongous

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Floating Point Types (Cont ..)

• A value with a decimal point stored as double
• Type can also be assigned explicitly
• Use F or f for a float
• 3.806e-3f or 0.003806f
• 3.806e-3F or 0.003806F
• Use L or l for a long double
• 7.16e-4l or 0.000716l
• 7.16e-4L or 0.000716L

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Comparison offloat and double
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Character Data Type

• Eight bits long
• Declared with char
• Used to store characters, but really numbers
  (integers)
• Can be
• signed char -128 to 127
• unsigned char 0 to 255

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Character Data Type (Cont ..)

• Some valid declarations
• char letter
• unsigned char index
• char topGrade A,
• bottomGrade F
• char topGrade 65,
• bottomGrade 70

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Variable Declaration Examples
16 Bits

• Examples
• short num
• short sum 120
• int product

product
num
16 bits
32 bits
120
sum
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Variable Names

• Length depends on compiler (at least 31)
• Characters allowed
• Alphabets A to Z, a to z
• Numeric 0 to 9
• The underscore character _
• Must begin with alpha or underscore
• C is case-sensitive
• Total is different from total and toTal

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Variable Names (Cont ..)

• Reserved words can not be used
• A list of reserved words is in Appendix (page
  786)
• Avoid naming variables with the same names as
  functions

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Variable Names (Cont ..)

• int xyz

float _x1y
starts with digit
short int 1sum
integer not a reserved word
int integer
"for" is a reserved word
double for
float SUM
int s123
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Variable Names (Cont ..)

• Use meaningful and descriptive variable names
• int s
• int sum

Avoid the first one and try to use the second one
if your variable is supposed to store the value
of some sum
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Variable Names (Cont ..)

• Begin a variable name with a lowercase letter
• Words after the first word in a variable name are
  capitalized

Good Names int test1, test2, test3 float
averageTestScore 0 int sumOfTests 0
Bad Names (but legal) int NumStudents float c,
d, e int average_grade
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Class Assignment 2

• Write a program that contains one double, one
  int, and one char.
• Store your height (to nearest half inch) in the
  double, the last digit of your phone number in
  the int, and your first initial in the char
• Print these values to the screen

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Constants

• Values can not be changed
• Can be defined/declared in two ways
• Using the define directive
• define PI 3.14159
• Declaring it with the reserved word const. In
  that case, it has to be initialized during
  declaration
• const int MAX_GRADE 100
• const double PI 3.14

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Constants (Cont ..)

• As with variables, use meaningful and descriptive
  names for constants
• Use all uppercase letters for the name of each
  constant
• Separate multiple words with underscore

Bad Names (but legal) const int
numOfStudents const float c define pi 3.14
Good Names const int NUM_OF_STUDENTS define
MAX_GRADE 100