Arrays

• Encountered already
• Example

  int ListOfNumbers[50]; 

• Subscripts start at 0 and end one less than the array size. In the above example valid subscripts range from 0 to 49.
• Access

  ThirdNumber = ListOfNumbers[2];
  ListOfNumbers[5] = 100; 

• A wise C guru (almost) always typedefs arrays
• ArrayTypedef.c - Counting character types in input

• Strings are defined as arrays of characters. For example, the following defines a string of 50 characters:

  char Name[50]; 

• In order to allow variable length strings the \0 character is used to indicate the end of a string.
• C has no string handling facilities built in and so the following are all illegal:

  char FirstName[50],LastName[50],FullName[100];
   
  FirstName = "Arnold"; //----Illegal
  LastName = "Schwarznegger"; //----Illegal
  FullName = "Mr"+FirstName+LastName; //----Illegal 

• There is a library of string handling routines defined in string.h, e.g.,
  • strcpy - copies a string into an array of char
  • strcat - appends a string into an array of char (there must be enough space allocated)
  • strlen - returns the length of the string (upto the first '\0' character)
  • strcmp and strcasecmp - compare two strings lexicographically
  • strstr - Looks for one string in another
• To print a string we use printf with a special %s control character:

  printf("%s",name); 

• Strings.c - String manipulation program

• A pointer to an array can be used as an array.
• A pointer to an \0 terminated array of characters is a string
  • That's how command line arguments work.

• Arrays may be initialised by following the definition with a list of initialisers enclosed in {} separated by commas.

  int TopTen[10] = {0,1,2,3,4,5,6,7,8,9};
            

• Character arrays may also be initialised with character strings. This adds a null at the end if the string is shorter than the array.

  char Name[32] = "Geoff Sutcliffe"; 

• If there are less initialisers than elements the extra elements are initialised with 0 if external or static, garbage if automatic. For example

  int Data[10] = {}; 

  initialises the entire array to 0/garbage.
• There may not be more initialisers than array elements.
• In the definition of an array the size may be implied by the initialisation list. e.g.

  int Data[] = {1,2,3,4,5,6}; 

  defines an array of size 6 and

  char Error[] = "Error\n"; 

  defines an array of size 7.

• In C multi-dimensional arrays are actually arrays of arrays (but not actually arrays of references/pointers).
• As [] are left-to-right associative int A[5][10]; defines an array of size 5 of (array of size 10).
• The right most subscript varies fastest in memory allocation.
• For access the indices are in separate brackets. e.g. A[3][5].
• There is no limit on the number of dimensions.
• Multi-dimensional array initialisation
  • As multi-dimensional arrays are arrays of arrays the initialisation uses the same principles as single dimension arrays.

    float Data[4][3] = {{1},{2},{3},{4}}; 
                   

    initilises the "first column" of data to 1,2,3,4 and the rest to 0 or garbage.
  • The rules for too few initialisers apply at any level.
• Array2D.c - Finding the day number in a year
• If multi-dimensional arrays are declared (e.g. when passed as function arguments, or in extern statements) all but the first dimension must be specified so the correct address arithmetic can be generated by the compiler. This is because the array is passed via the address of the first element, and it is necessary to know (only) how big each first dimension element is, but not how many there are, e.g.
• Array2DFunction.c - Finding the day number in a year
• A better approach is to use a typedef
• Array2DTypedef.c - Finding the day number in a year

• ArrayCrash.c

char *String1;
char String2[128];