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Structures

Data Structures & Algorithms. Structures. Structure. This is the second Data structure that we will study and one of the powerful features of C language (made obsolete by class in C++). Consider Student Data How to store names, age, address, city, CGPA for students?

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Structures

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  1. Data Structures & Algorithms Structures

  2. Structure • This is the second Data structure that we will study and one of the powerful features of C language (made obsolete by class in C++). • Consider Student Data • How to store names, age, address, city, CGPA for students? • Can u suggest how to create a database for it?

  3. Structure • A structure is an aggregate data structure used to keep different pieces of information together as a single data record. • A structure is like an array except that each element can have a different data type, and the elements in a structure have names instead of subscript values.

  4. Declaring a struct Variable • Syntax of the struct data type: • struct name { type field_name1; type field_name2; ... }; where • name is the name of the record type established by the struct, • each type field_name defines a field in the record, • the field definitions are separated by semicolons, and • the struct has a trailing semicolon.

  5. Example of Declaring a struct • /* declare a struct type (template) with name "Person_Record"*/ struct Person_Record { char name[20]; int age; }; /* Now, allocate memory */ struct Person_Record My_Record;/* a single record */ struct Person_Record PR_Array[100];/* an array of records */

  6. More About Structures • Normally structure is defined as global variable. • Its instances are created in main program or any other function. • The memory is not allocated when structure is defined. But when the instance of a structure is created then memory is reserved. • Hence structure is like a cookie mold!  with no cookies unless you put the mixture of ingredients…  • Hence structure stand alone is a template… and it cannot be initialized. You need to Instantiate it or declare a variable of type structure.

  7. Initializing a Structure Variable • To initialize a structure, follow the structure variable name with an equal sign, followed by a list of initialisers enclosed in braces. • Example: struct Person_Record My_record = { "Julie Dagg", 32 };

  8. Using a Structure Variable • There are two ways to reference (access) the fields in a structure: • The structure itself. • A pointer to the structure.

  9. I/O of Structures • When you use cin/cout you must read/write a structure field-by-field. • Emp.age = 20 • Cin >> emp.age • Cout << emp.age

  10. Structures as Function Parameters • The entire structure is copied to the function, i.e., a structure is passed by value. • A pointer to a structure can be passed to achieve call-by-reference. • Individual field of a structure can be passed as a real parameter to a function. • It is possible for a function to return a structure or a pointer to a structure.

  11. Examples • Passing an entire structure void func(Person_Record);//prototype of function ... Person_Record My_Record; func(My_Record);/* call-by-value */ • Passing a pointer to a structure void func(Person_Record *); ... Person_Record My_record; func(&My_record);/* call-by-reference , pointer*/ • Passing the address of a struct is faster, changes are reflected in My_Record

  12. Nested Structures • When one of the fields of a structure is itself a structure, it is called a nested structure. • Struct DateofBirth { int years; int months; int day; }; Struct Emp { char[25] name; DateofBirth Dob; };

  13. Self-Referential Structures(Will do in Detail in Coming Weeks) • We can declare pointers to structures that have not yet been declared. These are called dynamic data structures. • This permits us to create self-referential structures, as well as mutual-referential structures. • Example: struct listnode { int nodedata; struct listnode *nextnode; };

  14. Example Program • Here is a simple program

  15. do { cout << "Please enter Name of the employee" << endl; cin >> d[i].name ; cout << "Please enter age" << endl; cin >> d[i].age ; cout << "Please enter date (dd,mm,yyyy)" << endl; cin >> d[i].hireDate.dd; cin >> d[i].hireDate.mm; cin >> d[i].hireDate.yy; cout << "Would like to enter more data? (y/n)" << endl; i++; cin >> ch; } while (ch != 'n'); for (int j=0; j < i; j++) { cout << endl << d[j].name; } } #include <iostream.h> #include <conio.h> #include <stdio.h> struct Date{ int mm; int dd; int yy; }; struct data{ char name[25]; int age; struct Date hireDate; }; void main(void) { data d[20]; //creates array of type data with limit 20 int i = 0; char ch;

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