'C' Programming With Structure Records

1
'C' Programming With Structure Records

• Purpose of structures
• Coding a structure template
• Defining a new data type
• Functions which communicate using structures
• Use of structure pointers
• Structures and arrays
• Assigning structures

2
Purpose of structures

• Computing applications often need data of
  different kinds to be associated. A typical place
  where this occurs is in a record. For example a
  database record for a particular student might
  contain the student number, full name,
  course-code and year of entry.

3
Record declaration

• struct student
• char studno12
• char name50
• char course7
• int startyear

4
More examples

• struct coord float x,y
• struct complex float real,imaginary
• The data might have different types but does not
  have to be of different types. Structures also
  help with the naming of related parts of a record
  object.

5
Allocating memory to records

• The above declarations don't create any space for
  data storage, but they provide a template for
  data of the appropriate types to be allocated.
  Let's allocate some storage to data variables
• struct coord origin, cursor
• / 2 x-y coordinates called origin and cursor
  /
• struct student sdn_year250
• / array for 50 students /

6
Defining a new data type

• Better to have one word e.g. COORD to declare the
  type of data than 2 words e.g. struct coord .
  This needs a typedef statement
• struct coord float x,y
• typedef struct coord COORD
• / COORD now same as struct coord /
• COORD origin, cursor
• / declare 2 x-y coordinates called origin and
  cursor /

7
Use of the dot structure member access operator

• Members x and y of origin and cursor can now be
  accessed as origin.x, origin.y, cursor.x and
• cursor.y e.g.
• origin.x3.5
• origin.y2.0

8
Having defined a new data type

• We can declare stuctured data with a single word
  in a similar way that we use other built-in data
  types such as float and int. This simplification
  is useful as the name of the data type is going
  to appear in many places within our program, e.g.
  for declaring types of local data within
  functions or function parameters.
• It may not seem the case, but having many smaller
  functions which communicate cleanly is going to
  make programming much, much easier.

9
Functions which communicate using structured
parameters

• float distance(COORD a, COORD b)
• / calculate distance between a and b
  /
• float z,vert,horiz
• / z distance, vert y1 - y2,
  horiz x1 - x2 /
• horiza.x - b.x / the horizontal
  distance /
• verta.y - b.y / the vertical
  distance /
• / calculate z as the hypotenuse of a
  right angle triangle /
• zsqrt((horizhoriz) (vertvert)) /
  Pythagorus theorem /
• return z
  / zz xx yy /

10
Functions which communicate using structured
return values

• COORD getcoord(void)
• / note returned type is COORD
  /
• / prompts for and returns a coordinate /
• COORD temp
• printf("Enter x and y coordinates \n")
• scanf("ff",temp.x,temp.y)
• return temp

11
A program using distance and getcoord part 1

• include ltstdio.hgt
• include ltmath.hgt
• / needed to use sqrt() square root /
• struct coord float x,y
• / declare structure coord as having x and y
  members /
• typedef struct coord COORD
• / COORD is now same as struct coord /
• COORD origin, cursor
• / declare 2 x-y coordinates called origin and
  cursor /
• / function prototypes /
• float distance(COORD a, COORD b)
• COORD getcoord(void)

12
A program using distance and getcoord part 2

• int main(void)
• COORD origin, cursor
• float separation
• printf("enter details for origin\n")
• origingetcoord()
• printf("enter details for cursor\n")
• cursorgetcoord()
• separationdistance(origin,cursor)
• printf("the distance between origin and
  cursor is f\n",separation)
• return 0

13
Use of structure pointers

• Members x and y of coordinates a and b can also
  be accessed through pointers to a and b so that
  if pointer p stores the address of a pa then
• p-gtx
• directly accesses member x of a or a.x .

14
Rewrite the above program using pointers

• / declarations above here of headers , struct
  coord and typedef COORD same as before so not
  repeated /
• float distance(COORD a, COORD b)
• / a and b are now pointers to COORD /
• void getcoord(COORD t) / inputs coordinate
  through COORD pointer t /

15
Rewrite using pointers slide 2

• int main(void)
• COORD origin, cursor, orig,curs
• origorigin curscursor
• / store addresses in pointers orig and curs /
• float separation
• printf("enter details for origin\n")
• getcoord(orig)
• printf("enter details for cursor\n")
• getcoord(curs)
• separationdistance(orig,curs)
• printf("the distance between origin and
  cursor f\n" ,
• separation)
• getch()
• return 0

16
Rewrite using pointers slide 3

• float distance(COORD a, COORD b)
• / calculate distance between a and b /
• float z,vert,horiz / z distance,
  vert y1 - y2, horiz x1 - x2 /
• horiza-gtx - b-gtx / horizontal distance
  note -gt pointer syntax /
• verta-gty - b-gty / the vertical
  distance /
• / calculate z as the hypotenuese of a
  right angle triangle /
• zsqrt((horizhoriz) (vertvert)) /
  pythagorus theorem /
• return z /
  zz xx yy /
• void getcoord(COORD t) / inputs x-y coordinate
  using pointers /
• printf("please enter x and y
  coordinates\n")
• scanf("ff",t-gtx,t-gty) / -gt has
  higher precedence than /

17
Structures and arrays

• Having individual names for 10 coordinates is
  very awkward. We can declare the data as an
  array
• typedef struct coord float x,y COORD
• COORD graph10
• We can then assign members of our structure array
  like this
• graph9.x 12.5 graph9.y 7.3 / assign
  values to tenth element 9 of graph array /

18
Or we could input values into all coordinates
using a loop

• int i
• for(i0ilt10i)
• printf("Enter x value for coordinated\n"
  ,i1)
• scanf("f",graphi.x)
• printf("Enter y value for coordinated\n"
  ,i1)
• scanf("f",graphi.y)

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Or using structure pointer notation

• int i
• for(i0ilt10i)
• printf("Enter x value for coordinated\n"
  ,i1)
• scanf("f",(graphi)-gtx)
• / -gt has higher precedence than /
• printf("Enter y value for coordinated\n"
  ,i1)
• scanf("f",(graphi)-gty)

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A structure containing an array

• typedef struct student
• char name30
• float mark
• STUDENT
• STUDENT you
• printf ("enter name and mark\n")
• scanf ("sf",you.name,you.mark)
• / you.name is the address of the name array /
• / so no ampersand needed to get address/
• / BUT you.mark is not an array so needs /
• printf ("hello s your mark is f\n",you.name,you.
  mark)
• printf ("The first letter of your name is
  c\n",you.name0)

21
Assigning structures

• Unlike arrays, structures can be copied as a
  complete entity using a single assignment. This
  saves time. So instead of writing
• strcpy(temp.name,you.name)
• / use function strcpy to copy a string /
• temp.mark you.mark
• / can assign mark in one go /
• we can write
• tempyou / copy structure in one go /