Ch 1: Intro to Computer and Programming

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4
CHAPTER
Processing of Input and Output Functions and
Operators
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Objectives

• Output function
• Input function
• Character set
• Tokens
• Reserved words (keywords)
• Identifiers
• Constants
• String literals
• Punctuators
• Operators

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Input/output operations

• Input operation
• an instruction that copies data from an input
  device into memory
• Output operation
• an instruction that displays information stored
  in memory to the output devices (such as the
  monitor screen)
• The input/output operations are performed by C
  input/output functions.
• The standard C functions predefined in stdio.h
  header file include
• printf()
• scanf()
• getchar()
• putchar()

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The Output Function printf()

• Used to send data to the standard output (usually
  the monitor) to be printed according to specific
  format.
• Syntax
• printf(FormatControlString)
• printf(FormatControlString, PrintList)
• FormatControlString is a combination of
  characters, format specifier and escape sequence.
• PrintList is any constants, variables,
  expressions, and functions calls separated by
  commas.

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• Example
• printf(Thank you)
• printf(Total sum is d\n, SUM)
• d is a placeholder (format specifier)
• marks the display position for a type integer
  variable
• \n is an escape sequence
• moves the cursor to the new line

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Formatting Output

• Format specifier (placeholder)
• Tells the printf() function the format of the
  output to be printed put.

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• Examples

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• Escape Sequence
• is used in the printf() function to do something
  to the output.
• The common escape
• sequence
• and more
• (see Uckan pp. 729)

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Exercise

• Refer hand-outs.

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The Input Function scanf()

• Read data from the standard input device (usually
  keyboard) and store it in a variable.
• The general format is pretty much the same as
  printf() function.
• Syntax
• scanf(FormatControlString, InputList)
• InputList one or more variables addresses, each
  corresponding to a format specifier in the
  FormatControlString.
• One format specifier for each variable in
  InputList.
• The two or more variables in InputList must be
  separated by commas.
• Each element of InputList must be an address of a
  memory location (using prefix address operator)

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• Common format specifier used in printf() and
  scanf() functions.

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Example

• include ltstdio.hgt
• main()
• int Age
• printf(Enter your age )
• scanf(d, Age)
• printf(Your age is d,Age)
• Output?

Address operator
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• If you want the user to enter more than one
  value, you serialise the inputs.
• Example
• float height, weight
• printf(Please enter your height and weight)
• scanf(ff, height, weight)

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Exercise

• Refer hand-outs

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The getchar() and putchar() Functions

• getchar() - read a character from standard input
• putchar() - write a character to standard output
• Example
• include ltstdio.hgt
• main()
• char my_char
• printf(Please type a character )
• my_char getchar()
• printf(\nYou have typed this character )
• putchar(my_char)
• printf(\n)
• To be discussed in Chapter 9 Characters and
  Strings

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• Alternatively, you can write the previous code
  using normal scanf(), printf() and c format
  specifier.
• Example

include ltstdio.hgt void main(void) char
my_char printf(Please type a character )
scanf(c,my_char) printf(\nYou have typed
this character c , my_char)
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Character Set

• Characters are basic building blocks in C
  programs
• The C character set contains 92 characters
• Numeric digits (0-9)
• Letters of English alphabet (both a-z and A-Z)
• Space (blank)
• All other printable special characters on
  standard English keyboard , . ? / ( )
  lt gt etc EXCEPT , , and _at_

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Tokens

• Tokens are a series of continuous characters that
  compilers treat as separate entities.
• Tokens can be classified into
• Reserved words (also known as keywords)
• Identifiers
• Constants
• String Constants
• Punctuators
• Operators

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1. Reserved Words/Keywords

• Keywords that identify language entities such as
  statements, data types, language attributes, etc.
• Have special meaning to the compiler, cannot be
  used as identifiers in our program.
• Should be typed in lowercase.
• Must not be used as variables!!
• Keywords may be classified into
• Data type related
• Flow of control related
• Miscellaneous keywords

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Data Type Related Keywords

• A number of keywords are used to identify or
  qualify specific data types

• auto
• extern
• register
• static
• const
• char

• float
• int
• long
• short
• signed
• unsigned

• union
• void
• volatile
• struct
• double

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Flow of Control Related Keywords

• Keywords used for handling the flow of control in
  C programs

• break
• case
• goto
• continue
• default
• do

• while
• if
• else
• for
• switch
• return

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Miscellaneous Keywords

• The keywords that dont fall under either of the
  previous categories
• enum
• sizeof
• typedef

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2. Identifiers

• Words used to represent and reference certain
  program entities (variables, function names,
  etc).
• Also known as programmer-defined words.
• Example
• int my_name
• my_name is an identifier used as a program
  variable.
• void CalculateTotal(int value)
• CalculateTotal is an identifier used as a
  function name.

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Identifiers Rules
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Identifiers Naming Style

• Avoid excessively short and cryptic names such as
  x, or wt.
• Use reasonably descriptive name such as
  student_name and StudentID.
• Use userscores or capital letters to separate
  words in identifiers that consist of two or more
  words.
• Example StudentName, student_name, or
  studentname.

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Exercise

• Which are legal or illegal identifiers? Why?
• quiz grade
• Average
• Counter
• _sum
• dailyrate
• Text10
• 10thColumn
• continue

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Variables

• Variable ? a name associated with a memory cell
  which value can change
• Variable Declaration specifies the data type of
  a variable
• Example int num
• Variable Definition assigning a value to the
  declared variable
• Example num 5

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Basic Data Types

• There are 4 basic data types
• int
• float
• double
• char
• int
• To declare numeric program variables of integer
  type - whole numbers, positive and negative
• Example
• int number
• number 12

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• float
• fractional parts, positive and negative
• Example
• float height
• height 1.72
• double
• To declare floating point variable of higher
  precision or higher range of numbers -
  exponential numbers, positive and negative
• Example
• double valuebig
• valuebig 12E-3

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• char
• Equivalent to letters in English language
• Example of characters
• Numeric digits 0 - 9
• Lowercase/uppercase letters a - z and A - Z
• Space (blank)
• Special characters , . ? / ( )
  lt gt etc
• Single character
• Example
• char my_letter
• my_letter 'U'
• In addition, there are void, short, long, etc.

The declared character must be enclosed within a
single quote!
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Strings as a Derived Data Type

• A string is a sequence of characters that is
  treated as a single data item.
• In C a string variable is represented in a
  one-dimensional array of type char.
• The max length of the string constant that can be
  stored in a character array of size n is n-1
• string declared as one-dimensional array is
  always terminated by NULL or \0.
• Example
• char report_header41 Annual Report

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3. Constants

• Entities that appear in the program code as fixed
  values.
• Example
• const double INTEREST_RATE 0.015
• 4 types of constants
• Integer constants
• Floating-point constants
• Character constants
• Enumeration

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• Integer constants
• Positive or negative whole numbers with no
  fractional part
• Example
• const int MAX_NUM 10
• const int MIN_NUM -90
• Floating-point constants
• Positive or negative decimal numbers with an
  integer part, a decimal point and a fractional
  part
• Example
• const double VAL 0.5877e2
• (stands for 0.5877 x 102)

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• Character constants
• A character enclosed in a single quotation mark
• Example
• const char LETTER n
• const char NUMBER 1
• But, to print single quotation mark require
  backslash (known as escape sequence) since
  is illegal.
• printf(c, \)
• - prints a single quotation mark on screen
• printf(c, n)
• - prints the letter n on the screen
• printf(c, \n)
• move cursor to the beginning of a new line

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Example - 1
include ltstdio.hgt void main(void) const
double KMS_PER_MILES 1.609 double miles,
kms printf(Enter the distance in
miles) scanf(lf,miles) kms
KMS_PER_MILES miles printf(\nThat equals
f kilometer.\n , kms)
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Example - 2
include ltstdio.hgt define KMS_PER_MILES
1.609 void main(void) double miles,
kms printf(Enter the distance in
miles) scanf(lf,miles) kms
KMS_PER_MILES miles printf(\nThat equals f
kilometer.\n , kms)
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4. String Literals/ String Constants

• A sequence of any number of characters surrounded
  by double quotation marks .
• Example
• This is a string constant.
• Hello \John\.
• Example of usage in C program
• printf(My name is David Beckham.)
• simply print the string constant
• My name is David Beckham.
• Cannot print double quotation marks unless
  enclosed with backslashes.

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5. Punctuators (Separators)

• Symbols used to separate different parts of the C
  program.
• These punctuators include
• ( ) ,
• Usage example
• main()
• printf(Testing.)
• To be discussed when we come to the proper
  language feature in the coming chapters.

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6. Operators

• Tokens that result in some kind of computation or
  action when applied to variables or other
  elements in an expression.
• Example of operators
• - / lt gt
• Usage example
• result total1 total2

Chapter 5
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Summary

• Output function printf(), putchar()
• Input function scanf(), getchar()
• Multiple, wrapped lines
• Character set
• Tokens
• Reserved words (keywords)
• Identifiers including variables
• Constants
• String literals
• Punctuators
• Operators