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Data Structures

Data Structures. 1. Data Structures. Reference http://www.algolist.net. 2. Algorithm :- Outline the essence of a computational procedure , step by step instructions . Program :- an implementation of an algorithm in some programming language

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Data Structures

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  1. Data Structures 1

  2. Data Structures • Reference • http://www.algolist.net 2

  3. Algorithm :- Outline the essence of a computational procedure , step by step instructions . • Program :- an implementation of an algorithm in some programming language • Data Structure :- Organization of data needed to solve the problem . 3

  4. What is an Algorithm ? Algorithm: Finite set of instructions that, if followed, accomplishes a particular task. Describe: Representation of algorithm can written By :- in natural language ( English ) / pseudo-code / diagrams / etc. 4

  5. Any computing algorithm will have AT MOST five kinds of components: • Data structures to hold data • Instructions change data values • Conditional expressions to make decisions • Control structures to act on decisions • Modules to make the algorithm manageable by abstraction, i.e., grouping related components 5

  6. Relations between Problems, Algorithms and Programs Problem . . . . Algorithm Algorithm . . . . . . . . Program Program Program Program 6

  7. What is a Good Algorithm ? • Efficient :- • Running Time • Space Used • Efficiency as function of input size :- • The number of bits in an input number • Number of data elements ( numbers , points ) 7

  8. Worst- / average- / best-case • Worst-case running time of an algorithm • The longest running time for any input of size n • An upper bound on the running time for any input  guarantee that the algorithm will never take longer • Example: Sort a set of numbers in increasing order; and the data is in decreasing order • The worst case can occur fairly often • E.g. in searching a database for a particular piece of information • Best-case running time • sort a set of numbers in increasing order; and the data is already in increasing order • Average-case running time • Average number of steps taken on any instance • of size n 8

  9. Pseudo- code :- A mixture of natural language and high – level programming concepts that describes the main ideas behind a generic implementation of a data structure or algorithm Eg:- Algorithm arrayMax ( A, n ) input : An array A sorting n integers Output : The Maximum element in A currentMax A[0] for i 1 to n-1 do if currentMax < A[i] then currentMax A[i] return currentMax 9

  10. Pseudo – Code • It is more structured than usual language but less formal than a programming language . • Expressions : • Use standard mathematical symbols to describe numeric and Boolean expression . • Use for assignment ( “=“ in java ) • Use = for the equality relationship( “==“ in java ) 10

  11. Pseudo- Code • Programming Constructs :- • decision structures :- if …. Then … [ else ] • while – loops : while .. Do • repeat – loops : repeat … until .. • for – loop : for .. Do • array indexing : A[i] , A[I,j] • Methods : • Calls : object method ( args ) • returns : return value 11

  12. Simple Algorithm Find sum n numbers between any given range numbers 1- Start 2- Read N 3- Sum =0 4- For I= 1 to N 4.1 sum = sum + I 4.1 next I 5- print Sum 6- End 12

  13. Basic Structure of C++ Language Documentation Section Link Section Definition Section Global Declaration Section main(){ Declaration Section Executable Section } Subprogram Section Function 1 ….. Function n 13

  14. Language Built-in User-defined Data Operators Data Operators Assignment ( = ) Arithmetic (+,-,*,/,%) Relational (<, <=, >, >=,==,!=) Logical (&&, ||) Unary (++, --) Atomic int (2 bytes) char (1 byte) float (4 bytes) double (8 bytes) 14

  15. Tokens • The smallest element in the C language is the token. • Tokens can be: • Numeric constants : 123, 98.6, 1000000 • Character constants : ‘A’, ‘a’, ‘$’, ‘4’ • String constants : “UMBC”, “I like ice cream.”, “123”, “CAR”, “car” • Keywords : int , while, for • Names (identifiers) • Punctuation : ; : , ‘ “ [ ] { } ( ) • Operators: =, +, -, *, /, <>, <, >, >=, !=, &&, ||, ++, --

  16. Simple C++Program /*---- Hello World C Example ("hello.c") -------------------------------------*/ /* ANSI C Headers */ #include <iostream.h> /* Main Program starts here */ void main( ) { inti = 0; /* End of declarations ... */ for ( i = 0; i < 10; i++ ) { cout<<“Hello World”<<endl<< i ); /* print to standard output */ } } Include headers if you need to use functions in these files Comment: /* .. */ Declare all your variables first 15

  17. Control Statement 16

  18. Eg:- to calculate the average of n number • /*Calculate the average of n numbers*/ #include<iostream.h> void main(){ int n, count=1; float x, average,sum=0; cout<<"Enter the limit”<<endl; /*initialize and read in a value for n*/ cin>>n; while(count<=n) /*Read in the numbers*/ { cout<<"x= “; cin>>x; sum+=x; ++count; } /*calculate the average and display result*/ average=sum/n; cout<<“The average is ”<<average; getch();} 17

  19. While Syntax :- While (Expression ) { Statement (s ) Increment counter } Do – while Syntax :- Do { statement(s) Counter } While(expression ); 18

  20. Functions • A function is a self contained program segment that carries out some specific,well-defined task. • C regards main() as function • Functions should be defined separately before or after main. • A function will process information that is passed to it from the calling program and return a single value • Each function contains: • A function heading (function name), followed by optional list of arguments enclosed in parentheses. • A list of argument declarations • A compound statement enclosed within a pair of braces { } 19

  21. Functions Cont.. • Function Definition: returntypefn_name(type1 arg1,type2 arg2, …..type n,arg n) {localvariables functioncode } Example: int maximum(int x, int y) { int z; z=(x>=y) ? x:y; return(z);} • Calling A function: function-name(arg1,arg2,….arg n); • Function Prototype: returntypefn_name(type1 arg1,type2 arg2, …..type n,arg n);

  22. C ++ Program illustrating Function /*Program to calculate the area of a circle*/ #include <iostream.h> const float PI= 3.14; float areacircle( float radius) ; /* function prototype*/ main() { float radius, area; cout<<"Enter value of radius“<<endl; cin>>radius; area=areacircle(radius); /* call function */ cout<<“Area= “<<area ; getch(); } float areacircle(float r) { /* definition of function */ a= PI*r*r; return(a); } 20

  23. Assignment -1- • Write algorithm for the following • sum of n numbers between given range ( Using while ) • sum of n numbers between given range ( Using Do… while ) • count even& odd numbers in given range( Using For ) • count even & odd numbers in given range( Using while ) • count even & odd numbers in given range(Using Do.. while) 21

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