NCS 301 DATA STRUCTURE USING C

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1 NCS 301 Data Structure Using C NCS 301 DATA STRUCTURE USING C Unit-1 Part-1 Intro to Data Structures Hammad Mashkoor Lari Assistant Professor Allenhouse Institute of Technolgy 2 Introduction Data is the basic fact or identity that is utilized in calculation and manipulation. Data Numeric data Alphanumeric data Integers Floating point Data may be single value or it may be set of values. Whether it s a single value or a group of value, to be processed it must be organized in a particular fashion. Organization leads to structuring of data and hence our mission to study data structures. Subject Notes by Hammad Lari 1

2 NCS 301 Data Structure Using C 3 Data structure-definition In any area of application the input data and output data may each have a unique structure. Data structure is representation of logical relationship existing between individual elements of data. Data structure is way of organizing all data items that considers not only their storage but also their relationship to each other. Data structure can also be define as a mathematical or logical model of particular organization of data item. Data structure mainly specifies four things:- 1. Organization 2. Accessing 3. Degree of associativity 4. Processing alternatives for information Selection of a particular data structure stress on following:- 1. D.s must be rich enough in structure to reflect relationship between data 2. Structure should be simple so that it can be processed effectively whenever required 4 Classification Derived form primitive Emphasize on structuring of a group of homogeneous or heterogeneous data items. Basic data structures Directly operated upon by machine instructions Data structure Primitive Non primitive Integer Float Character Pointer Arrays Lists Files Linear Lists Non Linear Lists Stacks Queues Graphs Trees Subject Notes by Hammad Lari 2

3 NCS 301 Data Structure Using C 5 Memory Allocations in C Two types of memory allocations in C are: 1. Compile time or static allocation 2. Runtime or Dynamic Allocation (using pointers) Compile time:- Required amount of memory is allocated to program element at the start of program. Eg: int x,y;(2 bytes each) Integer Float Array of 5 int float a[5];(20 bytes) 2 Bytes 4 Bytes 10 Bytes Problems in static memory allocation Note:-there is no bound checking for array boundaries, i.e. If you have declared an array of five elements and by mistake you are intending to add more than five values in the array it will still work without error. 6 Problems in static memory allocation and its remedy as Dynamic Allocation For example:- int a[5]; For (i=0;i<10;i++) { scanf( %d,&a[i]); Problem is that the extra elements added as a part of this array a are not allocated the consecutive memory location after five elements. Its stored randomly at any unknown locations in the memory.so no access to these elements. Second problem is that if you store less number of elements than the number of elements for which you have declared memory then the rest of the memory will be wasted. This leads to inefficient use of memory. Runtime memory allocation: Allocating required amount of memory whenever needed. C provides following functions for allocation and de-allocation:- (i) malloc() (ii) calloc() (iii) free() (iv) realloc() Subject Notes by Hammad Lari 3

4 NCS 301 Data Structure Using C 7 malloc() Function Allocates a block of memory malloc() is like a request to the RAM to allocate memory. If request is granted it returns a pointer to the first block of that memory which is void else it returns null (fails to allocate memory) Header file:-alloc.h/stdlib.h(turboc) or malloc.h(unix) Syntax:- malloc(number of elements * size of each element); int *ptr; ptr=malloc(10*sizeof(int)); ptr=(int *)malloc(10*sizeof(int)); 20 bytes ///malloc returns a void pointer so casting is required If ptr==null it means memory is not allocated by RAM(grant failed). 8 Program to find sum and average of elements of array using malloc() #include<stdio.h> #include<conio.h> #define NULL 0 void main() { int *ptr, i, n, sum=0; float avg; Printf( Enter the no of elements ); Scanf( %d,&n); Ptr=(int*)malloc(n*sizeof(int)); If(ptr==NULL) { Printf( memory not available ); Getch(); Exit(0); Else{ Printf( enter the elemnts ); For(i=0; i<n; i++) Scanf( %d,ptr+i); For(i=0; i<n; i++) { Sum=sum+(*(ptr+i)); Printf( sum is %d,sum); Avg=sum/n; Printf( avg is %d,avg); Getch(); Example:- Output:- Enter the no of elements 5 Enter the element Sum is 108 Avg is 21.6 Subject Notes by Hammad Lari 4

5 NCS 301 Data Structure Using C 9 calloc(), free() & relloc() functions Synatx:- ptr_var=rellaoc(ptr_name,new_size); 10 Program for use of free() and realloc() Calloc() Works exactly similar to malloc() except for the fact that it needs two arguments. For example:- int *ptr; ptr=(int*)calloc(10,20); //2 specifies the type of byte and 10 specify number of elements Diffference between calloc() and malloc() Malloc() memory contains garbage values Calloc() memory contain all zeros. Free() Used to de-allocate the previously allocated memory using malloc() or calloc(). Syntax:- free(ptr_var); Relloc() Resize the size of memory block which is already allocated. #include<stdio.h> Output:- #include<conio.h> Msg is- data structure class #include<string.h> Void main() Msg is now- this is 2 nd yr cse class. ); { Char *msg; Msg=(char *)malloc(30*sizeof(char)); Strcopy(msg, data structure class ); Printf( msg is- %s \n,msg); Msg=(char*)realloc(msg,50); Strcopy(msg, this is 2 nd yr cse class. ); Printf( \n msg is now- %s,msg ); Free(msg); Getch(); Subject Notes by Hammad Lari 5

6 NCS 301 Data Structure Using C 11 Algorithms An algorithm is a set of rules for carrying out calculations either by hand or a machine. It is a sequence of computational steps that transform input into output. Algorithm is a branch of computer science that consists of designing and analysing computer programs. Design pertains to 1. Description of algorithm at an abstract level by means of pseudo language 2. Proof of correctness i.e.. Algorithm solves the given problem inall cases. Analysis deals with performance evaluation(complexity) Top down approach Algorithm Design Techniques Bottom up approach Algorithm design approaches 1. Incremental approach 2. Divide and conquer 3. Greedy 4. Dynamic programming 5. Backtracking 6. Branch and Bound 7. Randomized 12 Analysis Performance measurement Two types of metrics:- 1. Space complexity-amount of memory it needs to run to completion. 2. Time complexity-amount of time it needs to run to completion. Complexity of an algorithm is a function f(n) which measures the time and /or space used by an algorithm of input size n. Time space Trade-off A space-time or time-memory trade-off is a way of solving a problem or calculation in less time by using more storage space or memory or by solving a problem in very little space by spending a long time. It refers to a choice between algorithmic solutions of a data processing problem that allows one to decrease the running time of an algorithmic solution by increasing the space to store the data and vice versa. Types of analysis 1. Worst case running time 2. Average case running time 3. Best case running time Subject Notes by Hammad Lari 6

7 NCS 301 Data Structure Using C 13 Asymptotic Analysis Asymptotic analysis Our aim is not to count the exact number of steps of program or exact amount of time required for executing an algorithm. In theoretical analysis of an algorithm,it is common to estimate their complexity in asymptotic sense i.e.. To estimate the complexity function for reasonably large length of input n. Asymptotic Notation 1. Big Oh(O) notation 2. Omega (Ω) 3. Theta (Θ) Why asymptotic notation are imp? 1. They allow a simple characteristics of an algorithms efficiency. 2. They allow the comparison of performance of various algorithms. What does Asymptotic means? Asymptotic means a line that tends to converge to a curve which may or may not eventually touch the curve.it is a line that stays within bounds 14 Big Oh notation(upper bound) It gives an upper bound for a function to within a constant factor. We write f(n)=o(g(n)) if there are positive constants n0 and C such that to right of n0,the value of f(n) always lies on or below C(g(n)). O(1): function that runs in constant time O(n):functions that runs in linear time O(n 2 ):functions that runs in quadratic time O(Log n):functions that runs in logarithmic time Subject Notes by Hammad Lari 7

8 NCS 301 Data Structure Using C 15 Ω notation(lower bound) It gives an lower bound for a function to within a constant factor. We write f(n)= Ω(g(n)) if there are positive constants n0 and C such that to right of n0,the value of f(n) always lies on or above C(g(n)). 16 Θ notation(tightly bound) It bounds a function to within a constant factor. We write f(n)= Θ(g(n)) if there are positive constants n0,c1 and C2 such that to right of n0,the value of f(n) always lies between C1 g(n) and C2 g(n). Subject Notes by Hammad Lari 8

9 NCS 301 Data Structure Using C 17 Design Abstract data type A useful tool for specifying the logical properties of a data type is the ADT. A data type is the collection of values and a set of operations on those values. ADT refers to the basic mathematical concept that defines data type. ADT is defined as a mathematical model of the data objects that make up a data type as well as the functions that operate on these objects. ADT is a mathematical model with the collection of operations defined on that model. When we use ADT our programs divide into two pieces:- 1. Application-part that uses ADT 2. Implementation-part that implements ADT Applications Specification Uses the ADT Defines the ADT Implementation Implements the ADT 18 Data Structure operations Most common operations on data structure are- 1. Create 2. Select 3. Destroy 4. Update Other operations 1. Traversing 2. Searching 3. Inserting 4. Deleting 5. Sorting 6. Merging Subject Notes by Hammad Lari 9

10 NCS 301 Data Structure Using C 19 Practice Questions for C programming 1. Write a program to calculate factorial of a number N.(number being entered by user) 2. Write a program to print Fibonacci series up to N.(number being entered by user) 3. Write a program to print reverse of an integer number N. (number being entered by user) 4. Write a program to check if entered number N is a prime or not. 20 Class Website Subject Notes by Hammad Lari 10