1. Sudeshna Sarkar 7th March 2017
Structures
Sudeshna Sarkar
7th March 2017

2. Structure
Combine heterogeneous data to form a named collection

3. Structures: basics ideas
Structure = collection of variables
Members of a structure: variables in the collection
Structure = super variable, denotes the memory used for all members.
Each structure has a name, the name refers to the super variable, i.e. entire collection.
Each structure has a type: the type defines what variables there will be in the collection.

4. Structure types
You can define a structure type for each type of entity that you want to represent on the computer. “Programmer defined type”
Example: To represent books, you can define a Book structure type.
When you define a structure type, you must say what variables each structure of that type will contain.
Example: In a structure to represent books, you may wish to have variables to store the name of the book, its price, …

5. Defining a structure type
General form
struct structure-type{
member1-type member1-name;
member2-type member2-name; …
}; // Don’t forget the semicolon!
Example
struct Book{
char title[50];
double price; };
A structure-type is a user-defined data type, just as int, char, double are primitive data types.
Structure-type name and member names can be any identifiers.

6. Defines a new type E.g., Name of the type
struct motor { float volts; float amps; int phases; float rpm;
}; //struct motor
Name of the type
Note: name of type is optional if you are just declaring a single struct

7. struct Defines a new type E.g.,
struct motor { float volts; float amps; int phases; float rpm;
}; //struct motor
Members of the struct

8. Declaring struct variables
struct motor p, q, r;
Declares and sets aside storage for three variables , p, q, and r, each of type struct motor
struct motor M[25];
Declares a 25-element array of struct motor; allocates 25 units of storage, each one big enough to hold the data of one motor
struct motor *m;
Declares a pointer to an object of type struct motor

9. Example A structure definition: struct student {
char name[30];
int roll_number;
int total_marks;
char dob[10]; };
Defining structure variables:
struct student a1, a2, a3;
A new data-type

10. Structures Compound data: A date is struct ADate { int month; int day;
an int month and
an int day and
an int year
struct ADate {
int month;
int day;
int year; };
struct ADate date;
date.month = 9;
date.day = 1;
date.year = 2005;

11. Structure Representation & Size
struct CharCharInt {
char c1;
char c2;
int i;
} foo;
foo.c1 = ’a’;
foo.c2 = ’b’;
foo.i = 0xDEADBEEF;
sizeof(struct …) =
sum of sizeof(field)
+ alignment padding
Processor- and compiler-specific 62 61 EF BE AD DE c1 c2 i
padding
x86 uses “little-endian” representation

12. Members
struct name {
char first[10];
char midinit;
char last[20];
} sname, ename;
To access the members of a structure, we use the member access operator “.”.
strcpy (sname.first, “Aritra”);
sname.midinit = ‘K’;
strcpy (sname.last, “Saha”) ;

13. Defining a structure The composition of a structure may be defined as:
struct tag {
member 1;
member 2; :
member m; };
} variable_1, variable_2,…, variable_n;

14. typedef a typedef is a way of renaming a type struct name {
char first[10];
char midinit;
char last[20];
} ;
typedef struct name nameType;
nameType name1, name2;
typedef struct {
char first[10];
char midinit;
char last[20];
} NAMETYPE;
NAMETYPE sname, ename;

15. Processing a Structure
The members of a structure are processed individually, as separate entities.
A structure member can be accessed by writing
variable.member
Examples:
a1.name, a2.name, a1.roll_number, a3.dob

16. Operations on struct Copy/assign Get address Access members
struct motor p, q;
p = q;
Get address
struct motor p;
struct motor *s
s = &p;
Access members
p.volts;
(*s).amps; s->amps;

17. Things you can and can't do
Use = to assign whole struct variables
Have a struct as a function return type
You cannot
Use == to directly compare struct variables; can compare fields directly
Directly scanf or printf structs; can read fields one by one.

18. Operations on struct (function call)
Passing an argument by value is an instance of copying or assignment
Passing a return value from a function to the caller is an instance of copying or assignment
struct motor f (struct motor g) { struct motor h = g;
...;
return h; }

19. Struct initializers /* typedef structs go on top */
StudentRecord s1 = {"V Singhal", “17CS1002", 167, 8.31};
Using components of struct variables
s1.height = 169;
s1.cgpa = 8.4;
scanf ("%s", s1.rollno) ;

20. Example: Complex number addition
typedef struct {
float real;
float imaginary;
} complex;
int main( ) {
complex a, b, c;
scanf (“%f %f”, &a.real, &a.imaginary);
scanf (“%f %f”, &b.real, &b.imaginary);
c.real = a.real + b.real;
c.imaginary = imaginary + b.imaginary;
printf (“\n %f + %f j”, c.real, c.imaginary); }

21. Example: Complex number
#include <stdio.h>
typedef struct {
float real;
float imaginary;
} complex;
complex read_complex ( ) {
complex c;
scanf (“%f %f”, &c.real, &c.imaginary);
return c; }
void print_complex (complex c) {
printf (“ %f + i %f ”, c.real, c.imaginary);

22. Complex number arithmetic
complex add_complex (complex c1, complex c2) {
complex csum;
csum.real = c1.real + c2.real;
csum.imaginary = c1.imaginary + c2.imaginary;
return csum; }
complex sub_complex (complex c1, complex c2) {
complex cdiff;
cdiff.real = c1.real + c2.real;
cdiff.imaginary = c1.imaginary + c2.imaginary;
return cdiff;

23. Complex number arithmetic
complex mult_complex (complex c1, complex c2) {
complex cprod;
cprod.real =
cprod.imaginary =
return cprod; }
int main ( ) {
complex c1, c2, c3, c4;
read_complex (c1) ; read_complex (c2) ;
c3 = add_complex (c1, c2) ;
printf (“Sum of”) ;
print_complex (c1) ;
printf (“and”);
print_complex (c2);
printf(“is”) ;
print_complex (c3);

24. Arrays of Structures We can declare an array of structures.
struct student class[50];
The individual members can be accessed as:
class[i].name
class[5].roll_number

25. struct Arrays typedef struct { double x; double y; } point;
point pentagon[5];
struct Arrays
pentagon : an array of points x y
pentagon[1] : a point structure x y x y
pentagon[4].x : a double x y x y

26. Using Arrays of structs
StudentRecord class[MAXS]; …
for (i=0; i<nstudents; i++) {
scanf (“%d%d”, &class[i].midterm, &class[i].final);
class[i].grade =
(double)(class[i].midterm + class[i].final)/50.0; }

27. Passing Arrays of structs
An array of structs is an array.
When any array is an argument (actual parameter), its address is passed, not copied [as for any array]
int avg (StudentRec class[MAX]) {
... … }
int main ( ) {
StudentRec bt01[MAX];
int average;
...
average = avg_midpt(bt01) ;

28. A function using struct array
int fail (StudentRecord slist [ ]) {
int i, cnt=0;
for (i=0; i<CLASS_SIZE; i++)
cnt += slist[i].grade == ‘F’;
return cnt; }

29. Arrays within Structures
A structure member can be an array:
The array element within the structure can be accessed as: a1.marks[2]
struct student {
char name[30];
int roll_number;
int marks[5];
char dob[10];
} a1, a2, a3;

30. Structure within Structures
A structure member can be another structure:
struct college_info {
    int college_id;
    char college_name[50]; };
struct stud_detail {
    int class;
    char name[20];
    float percentage;
    struct college_info college;
} student_data;

31. typedef : An example typedef struct{ float real; float imag;
} COMPLEX;
COMPLEX a,b,c;

32. Structure Initialization
Structure variables may be initialized following similar rules of an array. The values are provided within the second braces separated by commas.
An example:
COMPLEX a={1.0,2.0}, b={-3.0,4.0};
a.real=1.0; a.imag=2.0;
b.real=-3.0; b.imag=4.0;

33. Parameter Passing in a Function
Structure variables could be passed as parameters like any other variable. Only the values will be copied during function invocation.
void swap(COMPLEX a, COMPLEX b) {
COMPLEX tmp;
tmp=a;
a=b;
b=tmp; }

34. An example program #include <stdio.h> typedef struct{
float real;
float imag;
} COMPLEX;
void swap(COMPLEX a, COMPLEX b) {
COMPLEX tmp;
tmp=a;
a=b;
b=tmp; }

35. Example program: contd.
void print(_COMPLEX a) {
printf("(%f , %f) \n",a.real,a.imag); }
main()
COMPLEX x={4.0,5.0},y={10.0,15.0};
print(x); print(y);
swap(x,y);

36. Returning structures
It is also possible to return structure values from a function. The return data type of the function should be as same as the data type of the structure itself.
COMPLEX add (COMPLEX a, COMPLEX b) {
COMPLEX tmp;
tmp.real = a.real+b.real;
tmp.imag = a.imag+b.imag;
return(tmp); }
Direct arithmetic
operations are not
possible with
Structure variables.

37. Example-1
Define a structure type student to store the name, roll, and total-marks of any student. Write a program to read this information (from keyboard) for one student and print the same on the screen.

38. Example-1
CODE:

39. Example-2
Use the same student structure as described in the Example-1. Define a function to check whether two students are same or not.
It returns 1, if the student1 and student2 are same
It returns 0, if the student1 and student2 are NOT same

40. Example-3
Write a C program to perform addition and multiplication of any two complex numbers, taken as input from the terminal.

41. Exercise Problems
Define a structure for representing a point in two-dimensional Cartesian co-ordinate system.
Write a function to compute the distance between two given points.
Write a function to compute the middle point of the line segment joining two given points.
Write a function to compute the area of a triangle, given the co-ordinates of its three vertices.

42. Problem Statement: Example 4
Write a program which reads two timestamps (hour, minute, second separately in 23:59:59 format) and prints the time difference between them.

43. Exercise 3 Define a structure data type named date containing three integer members: day, month, and year. Write a program to perform the following tasks:
To read data into structure members by a function
To print the date in the format: July 11, 2013
To validate the date by another function
Example Output:
Enter the day, month, and year:
The date is: September 10, 2016
It is a VALID date
Enter the day, month, and year:
The date is: April 31, 2015
It is an INVALID date

44. Exercise 4 Use the same date structure as defined in Exercise 1 to store date of birth and current date. Calculate the age of the person.