Lecture notes on Data structures and Algorithms and C

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C & Data Structures C & Data Structures P. S. Deshpande O. G. Kakde CHARLES RIVER MEDIA, INC. Hingham, Massachusetts Page 2/174 C & Data Structures Table of Contents CHAPTER 0: INTRODUTION..................................................................................................5 1. What This Book Is About ...............................................................................................5 2. What Do We Mean by Data?..........................................................................................5 3. Data Abstraction.............................................................................................................5 4. Data Structures................................................................................................................7 5. Overview of Data Structures.........................................................................................12 6. Exercises.......................................................................................................................13 E2. Write a program to finf maximum value of 4 numbers. Using 2 types of data structures: array of 4 numbers, 4 int numbers seperated........................................................................13 E3. Imagine a group of data you would like to put in a computer so it could be accessed and manipulated. For example, if you collect old CDROMs, you might want to catalog them so you could search for a particular author or a specific date... ................................................13 CHAPTER 1: C LANGUAGE .................................................................................................14 1. ADDRESS....................................................................................................................14 2. POINTERS...................................................................................................................15 3. ARRAYS......................................................................................................................16 4. ADDRESS OF EACH ELEMENT IN AN ARRAY....................................................17 5. ACCESSING AN ARRAY USING POINTERS .........................................................18 6. MANIPULATING ARRAYS USING POINTERS .....................................................19 7. ANOTHER CASE OF MANIPULATING AN ARRAY USING POINTERS ...........20 8. TWO-DIMENSIONAL ARRAY.................................................................................22 9. POINTER ARRAYS....................................................................................................24 10. STRUCTURES.........................................................................................................25 11. STRUCTURE POINTERS.......................................................................................26 12. Exercises...................................................................................................................27 CHAPTER 2: FUNCTION & RECURSION ...........................................................................30 1. FUNCTION..................................................................................................................30 2. THE CONCEPT OF STACK .......................................................................................31 3. THE SEQUENCE OF EXECUTION DURING A FUNCTION CALL......................32 4. PARAMETER PASSING.............................................................................................33 5. CALL BY REFERENCE..............................................................................................34 6. RESOLVING VARIABLE REFERENCES ................................................................35 7. RECURSION................................................................................................................36 8. STACK OVERHEADS IN RECURSION ...................................................................39 9. WRITING A RECURSIVE FUNCTION.....................................................................40 10. TYPES OF RECURSION ........................................................................................42 11. Exercises...................................................................................................................44 CHAPTER 3: SEARCHING TECHNIQUES ..........................................................................46 1. SEARCHING TECHNIQUES: LINEAR OR SEQUENTIAL SEARCH ...................46 2. BINARY SEARCH......................................................................................................48 3. Uses a recursive method to implement binary search...................................................52 4. COMPLEXITY OF ALGORITHMS...........................................................................52 5. Exercises.......................................................................................................................55 CHAPTER 4: SORTING TECHNIQUES................................................................................56 1. BUBBLE SORT...........................................................................................................56 2. INSERTION SORT......................................................................................................59 3. SELECTION SORT.....................................................................................................62 4. QUICK SORT...............................................................................................................64 5. Exercises.......................................................................................................................70 CHAPTER 5: STACKS AND QUEUES .................................................................................71 Page 3/174 C & Data Structures 1. THE CONCEPT OF STACKS AND QUEUES ..........................................................71 2. STACKS.......................................................................................................................71 3. APPLICATIONS OF STACKS...................................................................................78 4. QUEUES.......................................................................................................................83 5. IMPLEMENTATION OF QUEUES............................................................................85 6. IMPLEMENTATION OF A QUEUE USING LINKED REPRESENTATION.........88 7. APPLICATIONS OF QUEUES...................................................................................92 8. Exercises.......................................................................................................................96 CHAPTER 6: LINKED LISTS ................................................................................................97 1. THE CONCEPT OF THE LINKED LIST ...................................................................97 2. INSERTING A NODE BY USING RECURSIVE PROGRAMS .............................100 3. SORTING AND REVERSING A LINKED LIST.....................................................101 4. DELETING THE SPECIFIED NODE IN A SINGLY LINKED LIST.....................107 5. INSERTING A NODE AFTER THE SPECIFIED NODE IN A SINGLY LINKED LIST....................................................................................................................................110 6. INSERTING A NEW NODE IN A SORTED LIST..................................................114 7. COUNTING THE NUMBER OF NODES OF A LINKED LIST.............................118 8. ERASING A LINKED LIST......................................................................................121 9. CIRCULAR LINKED LISTS.....................................................................................124 10. DOUBLY LINKED LISTS ....................................................................................127 11. INSERTION OF A NODE IN A DOUBLY LINKED LIST .................................130 12. DELETING A NODE FROM A DOUBLY LINKED LIST .................................134 13. APPLICATION OF DOUBLY LINKED LISTS TO MEMORY MANAGEMENT 138 14. Exercises.................................................................................................................139 CHAPTER 7: TREES.............................................................................................................141 1. THE CONCEPT OF TREES......................................................................................141 2. BINARY TREE AND ITS REPRESENTATION .....................................................142 3. BINARY TREE TRAVERSAL .................................................................................146 4. BINARY SEARCH TREE .........................................................................................148 5. COUNTING THE NUMBER OF NODES IN A BINARY SEARCH TREE...........155 6. SEARCHING FOR A TARGET KEY IN A BINARY SEARCH TREE..................158 7. DELETION OF A NODE FROM BINARY SEARCH TREE ..................................162 8. AVL Tree....................................................................................................................170 9. Exercises.....................................................................................................................174 Page 4/174 C & Data Structures CHAPTER 0: INTRODUTION 1. What This Book Is About This book is about data structures and algorithms as used in computer programming. Data structures are ways in which data is arranged in your computer’s memory (or stored on disk). Algorithms are the procedures a software program uses to manipulate the data in these structures. Almost every computer program, even a simple one, uses data structures and algorithms. For example, consider a program that prints address labels. The program might use an array containing the addresses to be printed, and a simple for loop to step through the array, printing each address. The array in this example is a data structure, and the for loop, used for sequential access to the array, executes a simple algorithm. For uncomplicated programs with small amounts of data, such a simple approach might be all you need. However, for programs that handle even moderately large amounts of data, or which solve problems that are slightly out of the ordinary, more sophisticated techniques are necessary. Simply knowing the syntax of a computer language such as C isn’t enough. This book is about what you need to know after you’ve learned a programming language. The material we cover here is typically taught in colleges and universities as a second-year course in computer science, after a student has mastered the fundamentals of programming. 2. What Do We Mean by Data? When we talk about the function of a program, we use words such as "add," "read," "multiply," "write," "do," and so on. The function of a program describes what it does in terms of the verbs in the programming language. The data are the nouns of the programming world: the objects that are manipulated, the information that is processed by a computer program. In a sense, this information is just a collection of bits that can be turned on or off. The computer itself needs to have data in this form. Humans, however, tend to think of information in terms of somewhat larger units such as numbers and lists, so we want at least the human-readable portions of our programs to refer to data in a way that makes sense to us. To separate the computer's view of data from our own view, we use data abstraction to create other views. Whether we use functional decomposition to produce a hierarchy of tasks or object-oriented design to produce a hierarchy of cooperating objects, data abstraction is essential. Data abstraction The separation of a data type's logical properties from its implementation. 3. Data Abstraction Many people feel more comfortable with things that they perceive as real than with things that they think of as abstract. As a consequence, "data abstraction" may seem more forbidding than a more concrete entity such as an "integer." But let's take a closer look at that very concrete-and very abstract-integer you've been using since you wrote your earliest programs. Just what is an integer? Integers are physically represented in different ways on different computers. In the memory of one machine, an integer may be a binary-coded decimal. In a second machine, it may be a sign-and-magnitude binary. And in a third one, it may be represented in one's complement or two's complement notation. Although you may not know what any of these terms mean, that lack of knowledge hasn't stopped you from using integers. (You learn about these terms in an assembly Page 5/174 C & Data Structures language course, so we do not explain them here.) Figure shows several representations of an integer number. Figure: The decimal equivalents of an 8-bit binary number The way that integers are physically represented determines how the computer manipulates them. As a C++ programmer, you rarely get involved at this level; instead, you simply use integers. All you need to know is how to declare an int type variable and what operations are allowed on integers: assignment, addition, subtraction, multiplication, division, and modulo arithmetic. Consider the statement distance = rate time; It's easy to understand the concept behind this statement. The concept of multiplication doesn't depend on whether the operands are, say, integers or real numbers, despite the fact that integer multiplication and floating-point multiplication may be implemented in very different ways on the same computer. Computers would not be so popular if every time we wanted to multiply two numbers we had to get down to the machine-representation level. But that isn't necessary: C++ has surrounded the int data type with a nice, neat package and has given you just the information you need to create and manipulate data of this type. Another word for "surround" is "encapsulate." Think of the capsules surrounding the medicine you get from the pharmacist when you're sick. You don't have to know anything about the chemical composition of the medicine inside to recognize the big blue-and-white capsule as your antibiotic or the little yellow capsule as your decongestant. Data encapsulation means that the physical representation of a program's data is surrounded. The user of the data doesn't see the implementation, but deals with the data only in terms of its logical picture-its abstraction. Data encapsulation The separation of the representation of data from the applications that use the data at a logical level; a programming language feature that enforces information hiding If the data are encapsulated, how can the user get to them? Operations must be provided to allow the user to create, access, and change data. Let's look at the operations C provides for the encapsulated data type int. First, you can create ("construct") variables of type int using declarations in your program. Then you can assign values to these integer variables by using the assignment operator or by reading values into them and perform arithmetic operations using +, -, , /, and %. Figure shows how C has encapsulated the type int in a tidy package. Page 6/174 C & Data Structures Figure: A black box representing an integer The point of this discussion is that you have been dealing with a logical data abstraction of "integer" since the very beginning. The advantages of doing so are clear: You can think of the data and the operations in a logical sense and can consider their use without having to worry about implementation details. The lower levels are still there-they're just hidden from you. Remember that the goal in design is to reduce complexity through abstraction. We can extend this goal further: to protect our data abstraction through encapsulation. We refer to the set of all possible values (the domain) of an encapsulated data "object," plus the specifications of the operations that are provided to create and manipulate the data, as an abstract data type (ADT for short). Abstract data type (ADT) A data type whose properties (domain and operations) are specified independently of any particular implementation 4. Data Structures A single integer can be very useful if we need a counter, a sum, or an index in a program, but generally we must also deal with data that have lots of parts, such as a list. We describe the logical properties of such a collection of data as an abstract data type; we call the concrete implementation of the data a data structure. When a program's information is made up of component parts, we must consider an appropriate data structure. Data structures have a few features worth noting. First, they can be "decomposed" into their component elements. Second, the arrangement of the elements is a feature of the structure that affects how each element is accessed. Third, both the arrangement of the elements and the way they are accessed can be encapsulated. Data structure A collection of data elements whose organization is characterized by accessing operations that are used to store and retrieve the individual data elements; the implementation of the composite data members in an abstract data type Let's look at a real-life example: a library. A library can be decomposed into its component elements- books. The collection of individual books can be arranged in a number of ways, as shown in Figure. Obviously, the way the books are physically arranged on the shelves determines how one would go about looking for a specific volume. The particular library with which we're concerned doesn't let its patrons get their own books, however; if you want a book, you must give your request to the librarian, who retrieves the book for you. Page 7/174 C & Data Structures Figure: A collection of books ordered in different ways The library "data structure" is composed of elements (books) in a particular physical arrangement; for instance, it might be ordered on the basis of the Dewey decimal system. Accessing a particular book requires knowledge of the arrangement of the books. The library user doesn't have to know about the structure, however, because it has been encapsulated: Users access books only through the librarian. The physical structure and the abstract picture of the books in the library are not the same. The card catalog provides logical views of the library-ordered by subject, author, or title-that differ from its physical arrangement. We use the same approach to data structures in our programs. A data structure is defined by (1) the logical arrangement of data elements, combined with (2) the set of operations we need to access the elements. Page 8/174 C & Data Structures Notice the difference between an abstract data type and a data structure. The former is a high-level description: the logical picture of the data and the operations that manipulate them. The latter is concrete: a collection of data elements and the operations that store and retrieve individual elements. An abstract data type is implementation independent, whereas a data structure is implementation dependent. A data structure is how we implement the data in an abstract data type whose values have component parts. The operations on an abstract data type are translated into algorithms on the data structure. Another view of data focuses on how they are used in a program to solve a particular problem-that is, their application. If we were writing a program to keep track of student grades, we would need a list of students and a way to record the grades for each student. We might take a by-hand grade book and model it in our program. The operations on the grade book might include adding a name, adding a grade, averaging a student's grades, and so on. Once we have written a specification for our grade book data type, we must choose an appropriate data structure to implement it and design the algorithms to implement the operations on the structure. In modeling data in a program, we wear many hats. That is, we must determine the logical picture of the data, choose the representation of the data, and develop the operations that encapsulate this arrangement. During this process, we consider data from three different perspectives, or levels: 1. Application (or user) level: A way of modeling real-life data in a specific context; also called the problem domain 2. Logical (or abstract) level: An abstract view of the data values (the domain) and the set of operations to manipulate them 3. Implementation level: A specific representation of the structure to hold the data items, and the coding of the operations in a programming language (if the operations are not already provided by the language) In our discussion, we refer to the second perspective as the "abstract data type." Because an abstract data type can be a simple type such as an integer or character, as well as a structure that contains component elements, we also use the term "composite data type" to refer to abstract data types that may contain component elements. The third level describes how we actually represent and manipulate the data in memory: the data structure and the algorithms for the operations that manipulate the items on the structure. Let's see what these different viewpoints mean in terms of our library analogy. At the application level, we focus on entities such as the Library of Congress, the Dimsdale Collection of Rare Books, and the Austin City Library. At the logical level, we deal with the "what" questions. What is a library? What services (operations) can a library perform? The library may be seen abstractly as "a collection of books" for which the following operations are specified: • Check out a book • Check in a book • Reserve a book that is currently checked out • Pay a fine for an overdue book • Pay for a lost book How the books are organized on the shelves is not important at the logical level, because the patrons don't have direct access to the books. The abstract viewer of library services is not concerned with how the librarian actually organizes the books in the library. Instead, the library user needs to know only the correct way to invoke the desired operation. For instance, here is the user's view of the Page 9/174 C & Data Structures operation to check in a book: Present the book at the check-in window of the library from which the book was checked out, and receive a fine slip if the book is overdue. At the implementation level, we deal with the "how" questions. How are the books cataloged? How are they organized on the shelf? How does the librarian process a book when it is checked in? For instance, the implementation information includes the fact that the books are cataloged according to the Dewey decimal system and arranged in four levels of stacks, with 14 rows of shelves on each level. The librarian needs such knowledge to be able to locate a book. This information also includes the details of what happens when each operation takes place. For example, when a book is checked back in, the librarian may use the following algorithm to implement the check-in operation: All of this activity, of course, is invisible to the library user. The goal of our design approach is to hide the implementation level from the user. Picture a wall separating the application level from the implementation level, as shown in Figure 2.4. Imagine yourself on one side and another programmer on the other side. How do the two of you, with your separate views of the data, communicate across this wall? Similarly, how do the library user's view and the librarian's view of the library come together? The library user and the librarian communicate through the data abstraction. The abstract view provides the specification of the accessing operations without telling how the operations work. It tells what but not how. For instance, the abstract view of checking in a book can be summarized in the following specification: Page 10/174 C & Data Structures Figure: Communication between the application level and implementation level The only communication from the user into the implementation level occurs in terms of input specifications and allowable assumptions-the preconditions of the accessing routines. The only output from the implementation level back to the user is the transformed data structure described by the output specifications, or postconditions, of the routines. The abstract view hides the data structure, but provides windows into it through the specified accessing operations. When you write a program as a class assignment, you often deal with data at all three levels. In a job situation, however, you may not. Sometimes you may program an application that uses a data type that has been implemented by another programmer. Other times you may develop "utilities" that are called by other programs. In this book we ask you to move back and forth between these levels. Abstract Data Type Operator Categories In general, the basic operations that are performed on an abstract data type are classified into four categories: constructors, transformers (also called mutators), observers, and iterators. A constructor is an operation that creates a new instance (object) of an abstract data type. It is almost always invoked at the language level by some sort of declaration. Transformers are operations that change the state of one or more of the data values, such as inserting an item into an object, deleting an item from an object, or making an object empty. An operation that takes two objects and merges them into a third object is a binary transformer. Page 11/174 C & Data Structures An observer is an operation that allows us to observe the state of one or more of the data values without changing them. Observers come in several forms: predicates that ask if a certain property is true, accessor or selector functions that return a copy of an item in the object, and summary functions that return information about the object as a whole. A Boolean function that returns true if an object is empty and false if it contains any components is an example of a predicate. A function that returns a copy of the last item put into the structure is an example of an accessor function. A function that returns the number of items in the structure is a summary function. An iterator is an operation that allows us to process all components in a data structure sequentially. Operations that print the items in a list or return successive list items are iterators. Iterators are only defined on structured data types. In later, we use these ideas to define and implement some useful data types that may be new to you. First, however, let's explore the built-in composite data types C provides for us. Definition of Data Structure: An organization of information, usually in memory, for better algorithm efficiency, such as queue, stack, linked list, heap, dictionary, and tree, or conceptual unity, such as the name and address of a person. It may include redundant information, such as length of the list or number of nodes in a subtree. Definition of Algorithm: A computable set of steps to achieve a desired result. Note: Most data structures have associated algorithms to perform operations, such as search, insert, or balance, that maintain the properties of the data structure. The subjects of this book are data structures and algorithms. A data structure is an arrangement of data in a computer’s memory (or sometimes on a disk). Data structures include linked lists, stacks, binary trees, and hash tables, among others. Algorithms manipulate the data in these structures in various ways, such as inserting a new data item, searching for a particular item, or sorting the items. You can think of an algorithm as a recipe: a list of detailed instructions for carrying out an activity. 5. Overview of Data Structures Another way to look at data structures is to focus on their strengths and weaknesses. This section provides an overview, in the form of a table, of the major data storage structures discussed in this book. This is a bird’s-eye view of a landscape that we’ll be covering later at ground level, so don’t be alarmed if it looks a bit mysterious. Table shows the advantages and disadvantages of the various data structures described in this book. • A data structure is the organization of data in a computer’s memory (or in a disk file). • The correct choice of data structure allows major improvements in program efficiency. • Examples of data structures are arrays, stacks, and linked lists. • An algorithm is a procedure for carrying out a particular task. Page 12/174 C & Data Structures Algorithms + Data Structures = Programs Algorithms ↔ Data Structures 6. Exercises E1. Give an example of a relationship between Data Structure and Algorithm E2. Write a program to finf maximum value of 4 numbers. Using 2 types of data structures: array of 4 numbers, 4 int numbers seperated. E3. Imagine a group of data you would like to put in a computer so it could be accessed and manipulated. For example, if you collect old CDROMs, you might want to catalog them so you could search for a particular author or a specific date... Page 13/174 C & Data Structures CHAPTER 1: C LANGUAGE 1. ADDRESS Introduction For every variable declared in a program there is some memory allocation. Memory is specified in arrays of bytes, the size of which depending on the type of variable. For the integer type, 2 bytes are allocated, for floats, 4 bytes are allocated, etc. For every variable there are two attributes: address and value, described as follows: Program include stdio.h main () int i, j, k; //A i = 10; //B j = 20; //C k = i + j; //D printf ("Value of k is %d\n", k); Explanation Memory allocations to the variables can be explained using the following variables: 1. 100,i 10 2. 200, j 20 3. 300,k 30 When you declare variables i, j, k, memory is allocated for storing the values of the variables. For example, 2 bytes are allocated for i, at location 100, 2 bytes are allocated for j at location 200, and 2 bytes allocated for k at location 300. Here 100 is called the address of i, 200 is called address of j, and 300 is called the address of k. 4. When you execute the statement i = 10, the value 10 is written at location 100, which is specified in the figure. Now, the address of i is 100 and the value is 10. During the lifetime of variables, the address will remain fixed and the value may be changed. Similarly, value 20 is written at address 200 for j. During execution, addresses of the variables are taken according to the type of variable, that is, local or global. Local variables usually have allocation in stack while global variables are stored in runtime storage. Points to Remember • Each variable has two attributes: address and value. • The address is the location in memory where the value of the variable is stored. • During the lifetime of the variable, the address is not changed but the value may change. Page 14/174 C & Data Structures 2. POINTERS Introduction A pointer is a variable whose value is also an address. As described earlier, each variable has two attributes: address and value. A variable can take any value specified by its data type. For example, if the variable i is of the integer type, it can take any value permitted in the range specified by the integer data type. A pointer to an integer is a variable that can store the address of that integer. Program include stdio.h main () int i; //A int ia; //B i = 10; //C ia = &i; //D printf (" The address of i is %8u \n", ia); //E printf (" The value at that location is %d\n", i); //F printf (" The value at that location is %d\n", ia); //G ia = 50; //H printf ("The value of i is %d\n", i); //I Explanation 1. The program declares two variables, so memory is allocated for two variables. i is of the type of int, and ia can store the address of an integer, so it is a pointer to an integer. 2. The memory allocation is as follows: 3. i gets the address 1000, and ia gets address 4000. 4. When you execute i = 10, 10 is written at location 1000. 5. When you execute ia = &i then the address and value are assigned to i, thus i has the address of 4000 and value is 1000. 6. You can print the value of i by using the format %au because addresses are usually in the format unsigned long, as given in statement E. 7. Statement F prints the value of i, (at the location 1000). 8. Alternatively, you can print the value at location 1000 using statement G. ia means you are printing the value at the location specified by ia. Since i has the value for 1000, it will print the value at location 1000. Page 15/174 C & Data Structures 9. When you execute ia = 50, which is specified by statement H, the value 50 is written at the location by ia. Since ia specifies the location 1000, the value at the location 1000 is written as 50. 10. Since i also has the location 1000, the value of i gets changed automatically from 10 to 50, which is confirmed from the printf statement written at position i. Points to Remember 1. Pointers give a facility to access the value of a variable indirectly. 2. You can define a pointer by including a before the name of the variable. 3. You can get the address where a variable is stored by using &. 3. ARRAYS Introduction An array is a data structure used to process multiple elements with the same data type when a number of such elements are known. You would use an array when, for example, you want to find out the average grades of a class based on the grades of 50 students in the class. Here you cannot define 50 variables and add their grades. This is not practical. Using an array, you can store grades of 50 students in one entity, say grades, and you can access each entity by using subscript as grades1, grades2. Thus you have to define the array of grades of the float data type and a size of 50. An array is a composite data structure; that means it had to be constructed from basic data types such as array integers. Program include stdio.h main() int a5; \\A for(int i = 0;i5;i++) ai=i;\\B printarr(a); void printarr(int a) for(int i = 0;i5;i++) printf("value in array %d\n",ai); Explanation 1. Statement A defines an array of integers. The array is of the size 5—that means you can store 5 integers. 2. Array elements are referred to using subscript; the lowest subscript is always 0 and the highest subscript is (size –1). If you refer to an array element by using an out-of-range subscript, you will get an error. You can refer to any element as a0, a1, a2, etc. 3. Generally, you can use a for loop for processing an array. For the array, consecutive memory locations are allocated and the size of each element is same. Page 16/174 C & Data Structures 4. The array name, for example, a, is a pointer constant, and you can pass the array name to the function and manipulate array elements in the function. An array is always processed element by element. 5. When defining the array, the size should be known. Note The array subscript has the highest precedence among all operators thus a1 a2 gives the multiplication of array elements at position 1 and position 2. Points to Remember 1. An array is a composite data structure in which you can store multiple values. Array elements are accessed using subscript. 2. The subscript operator has the highest precedence. Thus if you write a2++,it increments the value at location 2 in the array. 3. The valid range of subscript is 0 to size −1. 4. ADDRESS OF EACH ELEMENT IN AN ARRAY Introduction Each element of the array has a memory address. The following program prints an array limit value and an array element address. Program include stdio.h void printarr(int a); main() int a5; for(int i = 0;i5;i++) ai=i; printarr(a); void printarr(int a) for(int i = 0;i5;i++) printf("value in array %d\n",ai); void printdetail(int a) for(int i = 0;i5;i++) printf("value in array %d and address is %16lu\n",ai,&ai); \\ A Page 17/174 C & Data Structures Explanation 1. The function printarr prints the value of each element in arr. 2. The function printdetail prints the value and address of each element as given in statement A. Since each element is of the integer type, the difference between addresses is 2. 3. Each array element occupies consecutive memory locations. 4. You can print addresses using place holders %16lu or %p. Point to Remember For array elements, consecutive memory locations are allocated. 5. ACCESSING AN ARRAY USING POINTERS Introduction You can access an array element by using a pointer. For example, if an array stores integers, then you can use a pointer to integer to access array elements. Program include stdio.h void printarr(int a); void printdetail(int a); main() int a5; for(int i = 0;i5;i++) ai=i; printdetail(a); void printarr(int a) for(int i = 0;i5;i++) printf("value in array %d\n",ai); void printdetail(int a) for(int i = 0;i5;i++) printf("value in array %d and address is %8u\n",ai,&ai); Page 18/174 C & Data Structures void print_usingptr(int a) \\ A int b; \\ B b=a; \\ C for(int i = 0;i5;i++) printf("value in array %d and address is %16lu\n",b,b); \\ D b=b+2; \\E Explanation 1. The function print_using pointer given at statement A accesses elements of the array using pointers. 2. Statement B defines variable b as a pointer to an integer. 3. Statement C assigns the base address of the array to b, thus the array's first location (a0) is at 100; then b will get the value 100. Other elements of the array will add 102,104, etc. 4. Statement D prints two values: b means the value at the location specified by b, that is, the value at the location 100. The second value is the address itself, that is, the value of b or the address of the first location. 5. For each iteration, b is incremented by 2 so it will point to the next array location. It is incremented by 2 because each integer occupies 2 bytes. If the array is long then you may increment it by 4. Points to Remember 1. Array elements can be accessed using pointers. 2. The array name is the pointer constant which can be assigned to any pointer variable. 6. MANIPULATING ARRAYS USING POINTERS Introduction When the pointer is incremented by an increment operator, it is always right incremented. That is, if the pointer points to an integer, the pointer is incremented by 2, and, if it is long, it is incremented by 4. Program include stdio.h void printarr(int a); void printdetail(int a); void print_usingptr(int a); main() int a5; for(int i = 0;i5;i++) ai=i; Page 19/174 C & Data Structures print_usingptr(a); void printarr(int a) for(int i = 0;i5;i++) printf("value in array %d\n",ai); void printdetail(int a) for(int i = 0;i5;i++) printf("value in array %d and address is %8u\n",ai,&ai); void print_usingptr(int a) int b; b=a; for(int i = 0;i5;i++) printf("value in array %d and address is %16lu\n",b,b); b++; // A Explanation 1. This function is similar to the preceding function except for the difference at statement A. In the previous version, b = b+2 is used. Here b++ is used to increment the pointer. 2. Since the pointer is a pointer to an integer, it is always incremented by 2. Point to Remember The increment operator increments the pointer according to the size of the data type. 7. ANOTHER CASE OF MANIPULATING AN ARRAY USING POINTERS Introduction You can put values in the memory locations by using pointers, but you cannot assign the memory location to an array to access those values because an array is a pointer constant. Program include stdio.h void printarr(int a); Page 20/174 C & Data Structures void printdetail(int a); void print_usingptr_a(int a); main() int a5; int b; int c; for(int i = 0;i5;i++) ai=i; printarr(a); b=2; \\ A b++; \\ B b=4; \\ C b++; b=6; \\ D b++; b=8; \\ E b++; b=10; b++; b=12; b++; a=c; //error \\F printarr(a); void printarr(int a) for(int i = 0;i5;i++) printf("value in array %d\n",ai); void printdetail(int a) for(int i = 0;i5;i++) printf("value in array %d and address is %16lu\n",ai,&ai); void print_usingptr_a(int a) Page 21/174