C Programming

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C Programming

• MIS 3013 003
• Mark Cornelius
• Lecture 10 Structures, Unions More

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Topics

• What is a Structure
• How are Structures implemented
• How do Structures Work
• The interesting details
• What is a union
• More about input and output
• More about Strings

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Topics cont.

• Miscellaneous functions with strings

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Structures

• A collection of variables
• Components, or members may be of different
  types (even arrays)
• The members are totally at the programmers
  discretion
• Most similar to a record in a database table.

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How are Structures Implemented?

• Structures must be defined!!!
• Here is an example
• Struct listing
• Int id_no
• Char lname20, fname20 e_mail20
• Now we have a structure called listing
• But we dont have any listings, because we did
  not declare any

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Implemetation

• We must now declare some variables that are of
  type listing.
• Struct listing record1, record2
• Now we have two variables that are of the
  structure we defined earlier
• We can address the members of the structure
  individually..

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Implementation

• Each listing we created, record1 record2,
  have members, i.e.
• Record1.id_no
• Record1.lnamex
• Record1.fnamex
• Record1.e_mailx
• Which are of the types specified in the
  definition of the structure.

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What does this mean?

• Now we can group related data under a SINGLE
  entity, regardless of the type!
• Note the similarity between a structure and a
  database record.
• Structures are the foundation for using linked
  lists.

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Structures and Arrays

• You can create an array of structures
• You can create a multidimensional array of
  structures (but why would you?)
• You can create pointers to structures
• You can create pointers to structures, that are
  MEMBERS of the structure being pointed to (this
  is how linked lists work)

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How do structures work

• Members of structures are accessed individually
  (similar to arrays
• You can perform any operation on a structure
  member that is legal for that type of data.
• You can pass structures, or individual members to
  functions

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Unions

• Unions are almost Identical to structures
• They have one key difference
• Only one member of a union can be accessed at a
  time
• This is because the members are stored together
  in memory
• With that said..

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DONT USE UNIONS

• that is, if you dont have to.
• I have spoken!

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Your mission

• To create an array of 5 structures that contains
  the following members
• Id_number (integer)
• Gpa (floating point)
• Read in the data from the keyboard.
• Display the result.
• You have 20 Minutes

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More on I/O

• Thats Input Output, my friend!

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More on input output

• When reading data from the keyboard, and
  displaying to the screen, we are working with 2
  files
• Stdin stdout
• These are called streams
• There are more streams, I.e. stderr, stdprn (the
  printer on lpt1)

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Standard Input

• Stdin stream
• Reading data from the keyboard
• Gets(), scanf(), getc(), getchar() all default to
  the standard input stream
• Fgetc() and fgets() are different why?

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Standard Output

• Stdout stream (the CRT Cathode Ray Tube a
  fancy acronym for MONITOR)
• Puts(), printf(), putc(), putchar() all default
  to the standard output stream
• Fputc(), fputs() are different why? (hint, it
  has to do with the letter F)
• You must learn the use of these commands, and
  they are explained in gory detail in chapter 14

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More about Strings

• Id stick around for this (especially if I
  planned on taking C)

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More about Strings

• We can do a lot of things with strings.we can
• Parse
• Search
• Concatenate
• Bring to uppercase
• Bring to lowercase
• Test for various conditions
• Determine the actual length of the string

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For example

• If lname20 is an array of characters, I.e. a
  string, and is all uppercase
• Strlwr(lname) makes it all lowercase
• We could even use isupper and test it.
• There are too many of these functions to
  memorize, which is why every sensible programmer
  always keeps a syntax guide handy!!!!

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What is the point?

• Point is, there are times when these functions
  come in handy, especially in PRODUCTION Systems