Arrays and Strings

1
Arrays and Strings
2
Derived Data Types

• Built from basic integer and floating- point
  data types.

• E.g.

• Arrays (holds several values of the same type)

• Strings (special array which can hold series of
  characters)

• Structures (holds several values of different
  types)

• Pointers (holds the address of an another
  variable)

• Classes (Sorry ?, we dont discuss about
  classes)

3
Arrays

• An array is a data form that can hold several
  values, all of one type.

• E.g. 1 An array of size 12 can be hold monthly
  sales figures.

• These sales figures are of the same type
  floating-point.

• Each value is stored in a separate array
  element.

• Computer stores all the elements consecutively
  in memory.

2nd element
1st element
12th element
4
Arrays

• An array declaration statement should indicate
  three things

• Type of value to be stored in each element.

• Name of the array.

• Number of elements in the array.

• E.g. float sales12

Data Type
Array name
Size of the array

11
1
2
10
0
sales

Sales0
Sales11
Sales1
Sales10
5
Arrays

• General Format

• data_type_name array_name array_size

• The size of the array must be a

• constant (E.g. 10)

• constant value (E.g. const int size 15)

• constant expression (E.g. sizeof(int) 5)

• Note Array size cannot be a variable.

• E.g.
• int size 5
• float birdsize //Invalid

6
Arrays

• To access each array element individually we
  use an index to number the array element.

• This numbering starts from 0 and cannot be
  changed.

• C uses array_name and bracket with the index
  to specify an array element.

• sales0 - 1st element , sales1 - 2nd
  element

• Each element can be treated like a simple
  variable.

• C also lets you initialize array elements
  within the declaration statement.

• E.g. int marks3 77, 60, 55

7
Arrays

• Rules on Array initialization

• You can use the initialization form only when
  defining the array.

• E.g. int x4 3, 6, 8, 10) // okay

• You cannot initialize it later.
• E.g. x4 3, 6, 8, 10 // not allowed

• You cannot assign one array wholesale to another.
• E.g. x y // not allowed

• You can use the initialization form only when
  defining the array.

• E.g. int x4 3,6

8
Arrays

• Rules on Array initialization

• int x 3, 6, 8, 10 //okay

• During initialization array size is optional.

• If you dont put the size, the compiler will do
  it for you.

9
Strings

• A string is a series of characters stored in
  consecutive bytes of memory.

• E.g. Rottweiler, Rhodesian Ridgeback, Ori Pei

• Can store in an array of char, with
  each character kept in its own array element.

• char dogBreed7 O, r, i, , P, e,
  i
• // not stored as a string

• But C needs one additional step to store this
  as a string.

• The null character \0, with ASCII code 0,
  should be added to the end of the string.

• This serves to mark the end of the string.

10
Strings

• E.g.
• char dogBreed8 O, r, i, , P ,
  e, i, \0
• //stored as a string

• This null character plays a fundamental role in
  C strings.

• Why do we need to add null character at the
  end of the string?

• C has many built -in functions that handle
  strings, including those used by cout.

• They all work by processing a string, character
  by character until they reach the null character.

• E.g. cout

• E.g. cout

11
Strings

• Earlier method to initialize a string variable
  looks tedious.

• Second method - another method for
  initializing strings.

• E.g. 1 char fish6 shark //reserve one
  character //for the null character

• The null character is automatically added to the
  string.

• E.g. 2 char fish shark

• The null character is automatically added to the
  string.

• Compiler counts the number of characters (plus
  null character) for you.

Note Do not interchange a string constant
(double quotes) with a character constant (single
quotes).
12
Strings Functions
(Defined in string.h header file.)

• strcat( s1,s2 ) - appends a copy of s2 to the end
  of string s1.

• strlen( s ) - counts all the visible characters
  in the string s and return this count.

• strcpy( s1, s2 ) copies string s2 to s1.

• strcmp( s1, s2 ) returns

• 0 if the strings s1 and s2 are the same

• 0 if s1 is lexicographically greater than s2

• Example

13
Cin and Strings

• To read a string from the keyboard we must
  enter the null character. But it is impossible.

• cin adds the null character to the string
  when it sees a white space character (space,
  tabs, carriage return).

• Thus, cin reads just one word.

14
Line Oriented Input

• getline( name, size ) takes to arguments

• name name of the array which hold the
  string

• size limit on the number of characters to be
  read

• E.g. cin.getline ( text, 20 )

• reads up to 19 characters, leaving room one
  element to hold the null character.

• stops reading input when it reaches this
  numeric limit or when it reads carriage
  return, whichever comes first.

15
Line Oriented Input

• cin.ignore (20, \n) takes to arguments

• causes up to 20 characters in the input stream
  to be skipped

• stops if the new line character is encountered.

16
2-D Arrays

• Data that is in rows and columns is usually
  stored in 2-dimensional arrays

• Declaring of 2-dimensional arrays

• Need to specify no of rows and columns

• int a3010 // int array of 30 rows and
  // 10 columns

• char ticTacToeBoard33 // three rows
  //and three columns of chars

17
2-D Arrays

• Unless specified, all initial values of arrays
  are garbage

• specify initial values by enclosing each row in
  curly braces

char ticTacToeBoard 3 3 'x', 'x',
'o',
'o', 'o', 'x',
'x', 'o', ' '

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Subscripting 2-D arrays

• int a3010

?
a00
a01
a02
a09
?
a11
a10
a12
a19
?
a22
a29
a20
a21
?
?
a290
a291
a292
a299