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Data structure with C 10CS35 unit-1
UNIT - 1 BASIC CONCEPTS
1.1 Pointers and Dynamic Memory Allocation
Pointers to data significantly improve performance for repetitive operations such as traversing strings, lookup tables, control tables and tree structures. In particular, it is often much cheaper in time and space to copy and dereference pointers than it is to copy and access the data to which the pointers point.Pointers are also used to hold the addresses of entry points for called subroutines in procedural programming and for run-time linking to dynamic link libraries (DLLs). In object-oriented programming, pointers to functions are used for binding methods, often using what are called virtual method tables.
Declaring a pointer variable is quite similar to declaring an normal variable all you have to do is to insert a star '*' operator before it.
General form of pointer declaration is -
where type represent the type to which pointer thinks it is pointing to.
Pointers to machine defined as well as user-defined types can be made
Pointer Intialization: variable_type *pointer_name = 0;
variable_type *pointer_name = NULL;
char *pointer_name = "string value here";
A pragmatic approach to algorithm specification and verification is presented. The language AL provides a level of abstraction between a mathematical specification notation and programming language, supporting compact but expressive algorithm description.
Proofs of correctness about algorithms written in AL can be done via an embedding of the semantics of the language in a proof system; implementations of algorithms can be done through translation to standard programming languages.
The proofs of correctness are more tractable than direct verification of programming language code; descriptions in AL are more easily related to executable programs than standard mathematical specifications. AL provides an independent, portable description which can be related to different proof systems and different programming languages.
Several interfaces have been explored and tools for fully automatic translation of AL specifications into the HOL logic and Standard ML executable code have been implemented. A substantial case study uses AL as the common specification language from which both the formal proofs of correctness and executable code have been produced.
1.3 Data Abstraction
Abstraction is the process by which data and programs are defined with a representation similar to its meaning (semantics), while hiding away the implementation details. Abstraction tries to reduce and factor out details so that the programmer can focus on a few concepts at a time. A system can have several abstraction layers whereby different meanings and amounts of detail are exposed to the programmer. For example, low-level abstraction layers expose details of the hardware where the program is run, while high-level layers deal with the business logic of the program.
1.4 Performance Analysis
Performance analysis involves gathering formal and informal data to help customers and sponsors define and achieve their goals. Performance analysis uncovers several perspectives on a problem or opportunity, determining any and all drivers towards or barriers to successful performance, and proposing a solution system based on what is discovered.
A lighter definition is:
Performance analysis is the front end of the front end. It's what we do to figure out what to do. Some synonyms are planning, scoping, auditing, and diagnostics.
What does a performance analyst do?
Here's a list of some of the things you may be doing as part of a performance analysis:
Interviewing a sponsor
Reading the annual report
Chatting at lunch with a group of customer service representatives
Reading the organization's policy on customer service, focusing particularly on the recognition
and incentive aspects
Listening to audiotapes associates with customer service complaints
Leading a focus group with supervisors
Interviewing some randomly drawn representatives
Reviewing the call log
Reading an article in a professional journal on the subject of customer service performance
Chatting at the supermarket with somebody who is a customer, who wants to tell you about her experience with customer service
We distinguish three basic steps in the performance analysis process:
data transformation, and
Data collection is the process by which data about program performance are obtained from an executing program. Data are normally collected in a file, either during or after execution, although in some situations it may be presented to the user in real time.
1.5 Performance Measurement
When you can measure what you are speaking about and express it in numbers, you know something about it.
You cannot manage what you cannot measure.
These are two often-quoted statements that demonstrate why measurement is important. Yet it is surprising that organisations find the area of measurement so difficult to manage.
In the cycle of never-ending improvement, performance measurement plays an important role in:
Identifying and tracking progress against organisational goals
Identifying opportunities for improvement
Comparing performance against both internal and external standards
Reviewing the performance of an organisation is also an important step when formulating the direction of the strategic activities. It is important to know where the strengths and weaknesses of the organisation lie, and as part of the ‗Plan Do Check Act cycle, measurement plays a key role in quality and productivity improvement activities. The main reasons it is needed are:
To ensure customer requirements have been met
To be able to set sensible objectives and comply with them
To provide standards for establishing comparisons
To provide visibility and a ―scoreboard‖ for people to monitor their own performance level
To highlight quality problems and determine areas for priority attention
To provide feedback for driving the improvement effort
It is also important to understand the impact of TQM on improvements in business performance, on sustaining current performance and reducing any possible decline in performance.