Character Processing

1
Chapter 5

• Character Processing

2
The Data Type char

• Each character is stored in a machine in one byte
  (8 bits)
• 1 byte is capable of storing 28 or 256 distinct
  values.
• When a character is stored in a byte, the
  contents of that byte can be thought of as either
  a character or as an integer.

3
The Data Type char

• A character constant is written between single
  quotes.
• a
• b
• A declaration for a variable of type char is
• char c
• Character variables can be initialized
• char c1A, c2B, c3

4
In C, a character is considered to have the
integer value corresponding to its ASCII
encoding. See page 609.
lowercase a b c ... z ASCII
value 97 98 99 ... 122 uppercase A B C ...
Z ASCII value 65 66 67 90 digit 0 1 2
... 9 ASCII value 48 49 50 ... 57 other
... ASCII value 38 42 43
5
Characters and Integers

• There is no relationship between the character
  2 (which has the ASCII value 50) and the
  constant number 2.
• 2 is not 2.
• A to Z 65 to 90
• a to z 97 to 112
• Examples
• printf(c,a)
• printf(c,97) have similar output.
• Printf(d,a)
• printf(d,97) have also similar output.

6
The Data Type char

• Some nonprinting and hard-to-print characters
  require an escape sequence.
• For example, the newline character is written as
  \n and it represents a single ASCII
  character.(page 176)
• Name of character Written in C Integer Value
• alert \a 7
• backslash \\ 92
• double quote \ 34
• horizontal tab \t 9

7
Input and Output of Characters

• getchar ( ) reads a character from the keyboard.
• c getchar() / variable c contains the
  next
  character of input /
• putchar ( ) prints a character to the screen.
• putchar(c) / prints the contents of the
  
  variable c as a character /

8
/ Illustrating the use of getchar( ) and
putchar( ) / include ltstdio.hgt int main
(void) char c while ((cgetchar()) !
EOF) putchar(c) putchar(c)
abcdef aabbccddeeff
EOF It is control-d in Unix control-z in DOS.
9
/ Capitalize lowercase letters and double
space / include ltstdio.hgt int main(void)
int c while ((cgetchar()) ! EOF) if
(a lt c c lt z) putchar(cA-a)
/convert to uppercase/ else if (c
\n) putchar (\n) putchar (\n)
else putchar (c)
cop3223!c C
10
Character Functions

• Function Nonzero (true) is returned if
• isalpha(c) c is a letter
• isupper(c) c is an uppercase letter
• islower(c) c is a lowercase letter
• isdigit(c) c is a digit
• isalnum(c) c is a letter or digit
• isspace(c) c is a white space character
• Function
  Effect_____________
• toupper(c) changes c to uppercase
• tolower(c) changes c to lowercase
• toascii(c) changes c to ASCII code

11
/ Capitalize lowercase letters and double space
/ include ltstdio.hgt includeltctype.hgt int
main(void) int c while ((cgetchar()) !
EOF) if (islower(c)) putchar(toupper(c))
/convert to uppercase / else if (c
\n) putchar (\n) putchar (\n)
else putchar (c)
12
Chapter 6

• The Fundamental Data Types

13
Size of Data Types in Unix

• char 1 byte
• short int 2 bytes
• int 4 bytes
• long int 4 bytes
• unsigned int 4 bytes
• float 4 bytes
• double 8 bytes
• long double 16 bytes
• 8 bits 1 byte

14
Data Type and Sizes

• Characters are treated as small integers.
• char c A / A has ASCII encoding 65
  /
• int i 65 / 65 is ASCII encoding for
  A /

0
1
0
0
0
0
0
1
15
Fundamental Data Types

• There are two types of representation for integer
  numbers
• unsigned
• signed

char unsigned char signed char
0 positive 1negative
int signed int unsigned int
0 positive 1negative
16
Data Types and Sizes

• int between 2,147,483,648 and 2,147,483,647 if
  (4-bytes)
• int between 32,768 and 32,767 if (2-bytes)
• There are a number of qualifiers that can be
  applied to these basic types. short and long can
  be applied to integers.
• short int sh
• long int counter
• The intent is that short and long should provide
  different lengths of integers where practical
  (i.e to save memory).
• Other qualifiers such as unsigned and signed may
  be applied to char or int.

17
The Floating Types

• A float on many machines has an approx. range of
  10-38 to 1038.
• A double on many machines has an approx. range of
  10-308 to 10308.
• The working floating type in C is double.

18
The sizeof Operator
include ltstdio.hgt int main() printf("Size
of some fundamental types computed. \n\n")
printf(" char3d byte \n",sizeof(char))
printf(" short3d byte \n",sizeof(short))
printf(" int3d byte
\n",sizeof(int)) printf(" long3d byte
\n",sizeof(long)) printf(" unsigned3d
byte \n",sizeof(unsigned)) printf("
float3d byte \n",sizeof(float)) printf("
double3d byte \n",sizeof(double))
printf("long double3d byte \n",sizeof(long
double)) return 0
19
Mathematical Functions

• There are no built-in mathematical functions in
  C.
• Functions such as
• sqrt( ) pow( ) exp( ) log( ) sin( )
  cos( )
• are available in the mathematical library
  (math.h).
• include ltmath.hgt
• The -lm option or some other option may be needed
  to compile a program that uses mathematical
  functions.

20
Mathematical Functions

• All of the functions listed on the previous
  slide, except the pow ( ) function, take a single
  argument of type double and return a value of
  type double.
• The pow ( ) function takes 2 arguments of type
  double and returns a value of type double.

21
Conversions

• Consider the following expressions.
• x y where x and y are of type int
• x y where x and y are of type short
• In both situations, xy is converted to int.
• If all the values of the original type can be
  represented by an int, the value is converted to
  an int otherwise it is converted to an unsigned
  int. (The integral promotion)

22
Arithmetic Conversions

• Arithmetic conversions can occur when the
  operands of a binary operator are evaluated.
• i f where i is an int and f is a float, the
  result is float
• See page 217 for a list of arithmetic conversion
  rules.

23
Examples
24
Type Casting

• In addition to implicit conversions, there are
  explicit conversions called casts.
• If i is an int, then
• (double) i
• will cast the value of i so that the expression
  has type double.
• Casts can be applied to expressions.
• x (float)((int)y1)
• y (float) i 3

25
Common errors

• Assume a 4-byte word machine
• int a 1, b 2147483648
• ab ? -2147483647
• Dividing two integers will always give an integer
• int j 2, k 5
• j/k ? 0
• (double) j/k ? 0.4

26
Chapter 7

• Enumeration Types and typedef

27
Enumeration Types

• Allows you to name a finite set and to declare
  identifiers, called enumerators, elements of the
  set.
• Consider the declaration
• enum day sun, mon, tue, wed, thu, fri, sat
• 
  0 1 2
  6
• To declare variables of type enum day
• enum day d1, d2
• To assign the value fri to d1
• d1 fri
• We can declare variables directly after the
  enumerator declaration.
• enum suit clubs1, diamonds, hearts,
  spades a, b, c

28
The Use of typedef

• C provides the typedef facility so that an
  identifier can be associated with a specific
  type.
• For example,
• typedef int color
• makes color a type that is synonymous with int,
  and it can be used in declarations just as other
  types are used.

29
The Use of typedef

• color red, blue, green
• enum bool false, true
• typedef enum bool boolean

30
/ Compute the next day / enum daysun, mon,
tue, wed, thu, fri, sat typedef enum day
day day find_next_day (day d) day
next_day switch(d) case
sun next_day mon
break case mon
next_day tue break
case sat
next_day sun break
return (next_day)
31
/ Compute the next day with a cast / enum day
sun, mon, tue, wed, thu, fri, sat typedef
enum day day day find_next_day (day d)
return ((day) ((int) d 1) 7))