CATEGORY OF FUNCTIONS

A function,depending on whether arguments are present or not whether a value is returned or not,may belong to one of the following categories.

category 1: Functions with no arguments and no return values.

category 2: Functions with arguments and no return value.

category 3: Functions with arguments and one return value.

category 4: Functions with no arguments but returns value.

category 5: Functions that return multiple values.

Functions with no arguments and no return values:

when a function has no arguments,it does not receive any data from the calling function.similarly,when it does not return a value,the calling function does not receive any data from the called function.In effect,there is no data transfer between the calling function and the called function.This is depicted in fig.1.The dotted lines indicate that there is only a transfer of control but not data.

As pointed out earlier, a function that does not return any value cannot be used in an expression.It can only be used as an independent statement.

It is important to note that the function value receives its data directly from the terminal.The input data include principle amount,interest rate and the period for which the final  value is to be calculated.

 Functions with arguments and no return value: 

the main function has no control over the way functions receive input data.for example,the function printline will print the same line each time is called.same is the case with the function value,we could make the calling function to read data from the terminal and pass it on to the called function.This approach seems to be wiser because the calling function can check for the validity of data,if necessary,before it is handed over to the called function.

The nature of data communication between the calling function and the function with arguments but no return value shown in fig.

Functions with arguments and one return value:

pointers in C language

A pointer is a derived data type in C.It is built from one of the fundamental data types available in C.Pointer contain memory addresses as their values.since these memory addresses are the locations in the computer memory where program instructions and data are stored,pointers can be used to access and manipulate data stored in the memory.

pointer are undoubtedly one of the most distinct and exciting features of C language.It has added power and flexibility to the language.Although they appear little confusing and difficult to understand for a beginner,they are a powerful tool and handy to use once they are mastered.

Pointers are used frequently in C,as they offer a number of benefits to the programmers.

They include:

1.pointer are more efficient in handling arrays and data tables.

2.Pointer can be used to return multiple values from a function via function arguments.

3.pointers permit reference to functions and thereby facilitating passing of functions as arguments to other functions.

4.The use of pointer arrays to character string results in saving of data storage space in memory.

5.pointers allow C to support dynamic memory management.

6.pointers provide an efficient tool for manipulating dynamic data structures such as structures,linked lists,queues,stacks and trees.

7.pointers reduces length and complexity of programs.

8.They increase the execution speed and thus reduce the program execution time.of course,the real power of C lies in the proper use of pointers. 

Types of errors in C language

There might be many other errors,some obvious and other not so obvious.All these errors can be classified under four types,namely,syntax errors,run-time errors,logical errors,and latent errors.

syntax error :

Any violation of rules of the language results in syntax errors.The compiler can detect and isolate such errors.when syntax errors are present,the compilation fails and is terminated after listing the errors and line numbers in the source program,where the errors have occurred. Remember,in some cases,the line number may not  exactly indicate the place of the error.In other cases,one syntax error may result in a long list of errors.Correction of one or two errors at the beginning of the program may eliminate the entire list.

Run-time errors:Errors such as a mismatch of data types or referencing an out-of-range array element go undetected by the compiler.A program with these mistakes will run,but produce erroneous results and therefore the name run-time errors.Isolating a run-time error is usually a difficult task.

Logical errors:As the name implies,these errors are related to the logic of the program execution.Such actions as taking a wrong path,failure to consider a particular condition,and incorrect order of evaluation of statements belong to this category.Logical  errors do not show uo as compiler-generated error messages.Rather,they cause incorrect translation of the algorithm into the program and a lack of clarity of hierarchy of operators.

consider the  following statement

if(x==y)

printf("they are equal \n");

when x and y are float types values,they rarely become equal,due to truncation errors.The printf call may not be executed at all.A test like while(x!=y)might create an infinite loop.

Latent errors:It is a  'hidden'error that shows up only when a particular set of data is used. For example,consider the following statement:

ratio=(x+y)/(p-q);

An error occurs only when p and q are equal. An error of this kind can be detected only by using all possible combinations of test data.

AIRLINES AND RAILWAYS TICKET RESERVATION

Indian Railways have introduced computerized ticket reservation system at many important stations.The computer stores all necessary information in connection with ticket reservation,such as train number,station enroute,distance,number of seats available for each train in each class,fare etc.It also stores information regarding persons who have already reservation such as name of the passengers,age,destination,date of journey,class,fare,etc.The person sitting at the counter gets information immediately whether seats on a particular date in a particular trains are available or not.it also gives information regarding train timings,train fares etc.on inquiry.

Computers are also used for plane tickets reservation.The passengers can also book tickets for onward journey if computers are connected in a computer network for such a purpose.They can also get informations about seats in hotels in other cities,climate of other cities etc.through the computer network.

                                                                                           

ARTIFICIAL INTELLIGENCE

A machine with reasoning,learning and logic capability is said to possess artificial intelligence.For example,expert systems posses artificial intelligence.An expert system is a software which utilizes a knowledge base collected from human specialists in a certain area,and helps users refer to this expertise in making their own decisions.

An artificial intelligence system has a knowledge base and programming technique to probe and process the facts in the knowledge base.The development of a knowledge base is very difficult and time consuming job.To develop a knowledge base the designers and research workers consult experts of a particular field.They collect facts that are based on the knowledge and experience of the experts in that field.such a collection forms knowledge base.An expert system uses a knowledge base for its artificial intelligence.Besides expert's knowledge an expert system also uses the decision rules of human specialists to reach certain conclusion and to give recommendations.Natural language may be used to input the user's facts and queries.The recommendation made by an expert system is based on the collection of information in the knowledge base.Hence,the knowledge base must be updates regularly.An expert system select one of many opinions depending on input data and information.The machine uses a set of decision rules on logical basis to choose an opinion.The machine is designed to perform such logical functions.It asks users to supply information on a problem.Computer then processes the information and reaches conclusion making use of the  knowledge base.

Due to  various many organizations want to develop expert systems.If an expert retires,dies or resigns the organization looses his expertise.So this is a very good reason to preserve expertise of experienced specialist's expertise.Some examples of expert systems are as follows.

Several expert systems in various specialized fields have been developed and diagnose diseases and recommend treatment.An expert system called HELP has been developed to diagnose heart diseases.Another  expert package is PUFF which has been designed to diagnose lungs diseases.The expert system CADUCEUS is a generalized package.It can process and evaluate over 4000 symptoms and other information to diagnose over 600 diseases. 

Fifth generation of computer

The fifth-generation computers are under development stage.Japan and USA have undertaken to design and develop such computers.These computers will use ULSI (ultra-large-scale integration) chips. ULSI chips contain millions of components into a single IC.such computers will use intelligent programming,knowledge-based problem solving techniques,high  performance multiprocessor system and improve human-machine interfaces.The input and output information for these computers will understand natual languages like, english,japanese,etc.The programmers will not have to learn programming languages.They will be able to speak commands or key information in their mother tongues.Visions system will also be incorporated. A computers will use intelligent software.The intelligent software will have artificial intelligence.In intelligent programming the user will tell the computer what to do.He will not tell the user will not have the burden of programming.

In the last 40 years there have been many innovations,inventions and developments in the field of computer technology but still today most of the computers use von Neumann's architecture of digital computer.The first four generations of computers used this basic structure and design in which a processor executes simple instructions in a sequence.In a fifth-generation of computers a different design and architecture may be used.in such a design data flow architecture will be used.There will be extensive use of parallel processing.Special coprocessors will be developed to make logical inference and manage massive amounts of stored knowledge.These computers will be acknowledge-based computers. PROLOG is expected to play an important role in making logical inferences.Users will work in natural language like English,Japanese,etc.The language of operating system will be PROLOG  

SINGLE-CHIP MICROCOMPUTERS (MICROCONTROLLERS)

With the development of VLSI technology it became possible to fabricate a digital computer on a single IC chip.A digital computer fabricated on a single IC chip is called single-chip microcomputer.since it is widely used for control application,it is called microcontroller. It is very small and compact.It forms the part of the devices or equipment which is to be controlled.It is used for industrial control,process control,consumer and appliances control,instrumentation,etc.it contains a CPU,memory (RAM,and ROM/EPROM) and I/O lines.A powerful microcontroller may contain some other components which are needed for control application such as analog-to-digital converter,digital-to-analog converter,interrupt controller,DMA controller,wave generator,etc.

Intel developed 8-bit microcontrollers 8051 series was developed.8-bit microcontrollers are used for simple and low-cost control applications.In 1983,Intel developed 16-bit microcontrollers,8096 series.Later on,it developed 80196 series of 16-bit microcontrollers. These were more powerful and were used in sophisticated industrial control,intelligent computer peripherals,instrumentation,etc.

Other manufactures also developed 4-bits,8-bits,16-bit and 32-bit microcontrollers.Motorola developed 32-bit microcontrollers are used for complex control applications.