1. Slide 1 of 31Ver. 1.0
Programming in C
In this session, you will learn to:
Work with structures
Use structures in file handling
Objectives

2. Slide 2 of 31Ver. 1.0
Programming in C
Working with Structures
Structures:
Are collection of heterogeneous data types.
Are also known as records.
Are used to define new data types.
Are defined using the struct keyword.

3. Slide 3 of 31Ver. 1.0
Programming in C
Defining Structures
A structure is defined by using the struct keyword.
Consider the following example:
struct {
char transno [4];
int salesno;
int prodno;
int unit_sold;
float value_of_sale;
} salesrec;
All the variables in the record are treated as one data structure –
salesrec.

4. Slide 4 of 31Ver. 1.0
Programming in C
Practice: 7.1
1. State whether True or False:
The members of a structure must be of the same data type.
1. a. Give the declaration for a structure called date with the
following members.
day (2 digits)
month (2 digits)
year (4 digits)
b. Give appropriate statements to accept values into the
members of the structure date and then print out the
date as mm/dd/yyyy.

5. Slide 5 of 31Ver. 1.0
Programming in C
Solution:
1. False
2. a. The structure declaration should be:
struct {
int day;
int month;
int year;
} date;
b. The statements could be:
scanf(“%d%d%d”, &date, &date.month, &date.year);
printf(“%d/%d/5d”, date.month, date.day,
date.year);
Practice: 7.1 (Contd.)

6. Slide 6 of 31Ver. 1.0
Programming in C
Defining a label structures:
Structure label may be declared as:
struct salesdata {
char transno [4];
int salesno;
int prodno;
int unit_sold;
float value_of-sale;
};
struct salesdata salesrec;
Here, salesdata is the label and salesrec is the data item.
Defining Structures (Contd.)

7. Slide 7 of 31Ver. 1.0
Programming in C
Practice: 7.2
Given the following declarations:
struct date_type{ struct {
int day; int day;
int month; int month;
int year; int year;
}; } date;
Declaration 1 Declaration 2
Answer the following questions:
1. Memory is allocated for the structure (date_type/ date).
2. Which of the following is/are the correct way(s) of referring to
the variable day?
a. day.date
b. date_type.day

8. Slide 8 of 31Ver. 1.0
Programming in C
Practice: 7.2 (Contd.)
3. What change(s) should be made to the first declaration so that
the structure date is created of type date_type?
4. Is the following statement valid in case of the second
declaration? If not, why?
struct date another_date;

9. Slide 9 of 31Ver. 1.0
Programming in C
Solution:
1. date (date_type is only a structure type)
2. a. Invalid because the structure name precedes the variable
name.
b. Invalid because date_type is not actually created in
memory, it is only a label.
3. The following statement should be added after the struct
declaration:
struct date_type date;
4. This is invalid because date is not a structure type but an
actual structure in memory.
Practice: 7.2 (Contd.)

10. Slide 10 of 31Ver. 1.0
Programming in C
Passing Structures to Functions
Passing Structures to Functions:
Structures may be passed to functions either by value or by
reference.
Usually methods pass the address of the structure.
The name of the variable being referenced is preceded by the
symbol .

11. Slide 11 of 31Ver. 1.0
Programming in C
Practice: 7.3
1. Consider the following code:
struct date_type {
int day;
int month;
int year;
}; struct date_type date, *ptr;
a. How can the pointer variable ptr be assigned the address of
the structure date?
b. Is the following statement valid?
ptr = &date_type;
c. Give alternative ways of referring to:
i. &date.day
ii. date.month
Given that ptr has been assigned the address of the structure
date.

12. Slide 12 of 31Ver. 1.0
Programming in C
Practice: 7.3 (Contd.)
2. Consider the incomplete code of a program that is given in
the following file. The code uses a function called
printmonth() that displays the month name
corresponding to any month number. The month number is
accepted into the member month of the structure date. The
blanks have to be filled in appropriately.
Microsoft Office
Word 97 - 2003 Document

13. Slide 13 of 31Ver. 1.0
Programming in C
Solution:
1. a. By using the following statement:
ptr = &date;
b. No. because date_type is not created in memory; it is
only a label.
c. i. &(ptr-> date)
ii. ptr-> month
2. The statement to invoke printmonth() could be:
printmonth(&date); /*invoke printmonth() by
passing structure */
The missing lines in the code for printmonth() are:
printmonth(point)
struct date_type *point;
point is the parameter of the function since it is used within
the function to access members of the structure date.
Practice: 7.3 (Contd.)

14. Slide 14 of 31Ver. 1.0
Programming in C
Arrays of Structures
Arrays of structures can also be created.
It works in the same way as any other data type array.
Consider the following example:
struct prod data{
char prodname[8];
int no_of_sales;
float tot_sale;
};
An array for the preceding structure can be declared as:
struct proddata prod_field[4];
The elements of the structure can be accessed as:
prod_field [0].prodnam[0];

15. Slide 15 of 31Ver. 1.0
Programming in C
Practice: 7.4
1. Declare a structure which will contain the following data for
3 employees:
Employee code (3 characters)
First name (20 characters)
Middle initial (1 character)
Last name (20 characters)
The employee codes to be stored in this structure are E01,
E02, and E03.
2. Write the code to input for all 3 employees, and print out the
initials of each (e.g. Ashraf A Kumar would be printed as
AAK) along with their codes.

16. Slide 16 of 31Ver. 1.0
Programming in C
Solution:
Practice: 7.4 (Contd.)
Microsoft Office
Word 97 - 2003 Document

17. Slide 17 of 31Ver. 1.0
Programming in C
Working with Structures (Contd.)
A structure can be used as a valid data type within another
structure. For example, if date has been defined as:
struct date{
int dd;
int mm;
int yy;
};
The date structure can be used in another structure as:
struct trans_rec{
char transno[4];
char type;
float amount;
struct date tran_date;
};

18. Slide 18 of 31Ver. 1.0
Programming in C
Practice: 7.5
1. What will the following declaration do?
typedef char sentence[50];
sentence complex[10];

19. Slide 19 of 31Ver. 1.0
Programming in C
Solution:
1. The first statement defines sentence as a data type consisting
of an array of 50 characters. The second statement declares
complex as a two-dimensional array, (an array of ten arrays of
50 characters each).
Practice: 7.5 (Contd.)

20. Slide 20 of 31Ver. 1.0
Programming in C
Using Structures in File Handling
To store data permanently, it needs to be stored in a file.
Mostly, the data, to be written in the file, is a logical group of
information i.e. records.
These records can be stored in structure variables. Hence,
you need to write structures onto a file.

21. Slide 21 of 31Ver. 1.0
Programming in C
Writing Records onto a File Using Structures
The fwrite() function is used to write structures onto a
file.
The fwrite() function has the following syntax:
fwrite (constant pointer, sizeof (datatype), 1,
FILE pointer);
The first parameter is a pointer to the data to be written.
The second parameter is the size of data to be written.
The third parameter is the number of objects or data to be
written.
The fourth parameter is the pointer to file.

22. Slide 22 of 31Ver. 1.0
Programming in C
Practice: 7.6
Now that various assets of the transaction data entry
program have been explained, these have to be
consolidated and the entire program coded. The problem
statement is repeated below.
A transaction data entry program called dataent, used at
the familiar Alcatel Automatics Company, has to be coded.
The transaction file stores the data on transactions made by
the salesmen of the company. The records consist of the
following fields.
Transaction number
Salesman number
Product number (numbered 1 to 4)
Units sold
Value of sale
Value of sale is calculated in the program.

23. Slide 23 of 31Ver. 1.0
Programming in C
Practice: 7.6 (Contd.)
The program should allow the user to indicate when he
wants to stop data entry (i.e. it should keep accepting
records until the user indicates that there are no more
records).
After all records have been entered, a report on the total
number of sales and the total sale value for each product is
to be printed in the following format (for each product).
Product number : ___________________
Product name : ___________________
Total number of sales : ___________________
Total sale value : ___________________
Use the structures salesrec, salesdata, prodata, and
prod_field defined earlier and code for the report printing
within main(). Also use the code provided on page 7.2 and
7.3 in your solution.

24. Slide 24 of 31Ver. 1.0
Programming in C
Solution:
Practice: 7.6 (Contd.)
Microsoft Office
Word 97 - 2003 Document

25. Slide 25 of 31Ver. 1.0
Programming in C
Reading Records from Files Using Structures
The fread() function is used to read data from a stream.
The fread() function has the following syntax:
fread (ptr, sizeof, 1, fp);
The first parameter is a pointer to the variable where the data
is to be fetched.
The second parameter is the size of data to be read.
The third parameter is the number of objects or data to be
read.
The fourth parameter is the pointer to file.

26. Slide 26 of 31Ver. 1.0
Programming in C
Practice: 7.7
1. Is the following statement to read the first 5 records of the
file trans.dat valid?
fread (ptr, (sizeof(salesrec) *5), 1, fp);
If not state why and give the correct statement. No checks
are to be done for an unsuccessful read.
2. Modify the above fread() statement to include an end-of-
file check and also check whether the records have been
read successfully. In case of end-of-file, display the
message:
End-of-file encountered
and in case of other errors, display the message and exit:
Unsuccessful read
In case of a successful read, display the salesman number
and transaction number of each record. Give all the
structure declarations required.

27. Slide 27 of 31Ver. 1.0
Programming in C
Solution:
Practice: 7.7 (Contd.)
Microsoft Office
Word 97 - 2003 Document

28. Slide 28 of 31Ver. 1.0
Programming in C
Practice: 7.8
1. Debug the following program called dat.c using the error
listing provided in the following file.
Microsoft Office
Word 97 - 2003 Document

29. Slide 29 of 31Ver. 1.0
Programming in C
Solution:
1. The solution to this practice will be discussed in class. Work
out your answer.
Practice: 7.8 (Contd.)

30. Slide 30 of 31Ver. 1.0
Programming in C
Summary
In this session, you learned that:
Records can be defined in C by using structures.
Structure members can be of the same/different data type.
Memory is not reserved when a structure label is declared. A
structure is created when it is declared as a struct of the
same type as the structure label.
A member of a structure can be accessed as follows:
structure-name.member-name
A pointer to a structure can be used to pass a structure to a
function. Using pointers, the structure members are accessed
as follows:
pointer-name->member-name
Arrays of structures can be defined and initialized (if global or
static). To access any member, an index has to be used after
the structure name, as follows:
structure-name [index ].member-name

31. Slide 31 of 31Ver. 1.0
Programming in C
Summary (Contd.)
The typedef statement can assign names to user-defined
data types. These are treated the same way as data types
provided by C.
The fread() function can read records from a file into a
structure/array of structures. The format of the function is:
fread (pointer, size of structure, number of
objects to be read, file pointer);
The fread() function returns the number of objects read from
the file. It does not return any special value in case of
end-of-file. The feof() function is used in conjunction with
fread() to check for end-of-file.
The fwrite() function can write a structure array of
structures onto a file. All numeric data is written in compressed
form. Usually, fread() and fwrite() are used in
conjunction.