Introduction. Basic computer operations: Application of computer:

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1 Introduction The term computer is derived from the word compute, which means to calculate. A computer is an electronic machine which performs calculation and controlling operation, that can be expressed either in logical or numerical terms. A computer is an electronic device, which performs various operations with the help of instructions to process the information in order to achieve desired results. A computer is an electronic device which converts raw data into valid (or) meaningful information. Data: It is the raw material, that user gives as input. Information: It is the processed data and the information comes in various forms depending upon the application. Basic computer operations: Input: It is the process of capturing the raw data (user input). Process: It is the process of converting data into information. Output: It is the result of the transformation process. Storing: It is the process of saving the data or information for future requirement. Controlling: It is the process of directing the methods and sequencing the operation. Application of computer: The computer is normally a calculating device that can perform any operations at enormous speed. Computer in Business: The main objective of business is transaction processing with suppliers, employers, customers. Financial analysis is performed throughout company. Computers in Industry: Products are designed and manufactured. CAD (computer aided design) is used to develop products and CAM (computer aided manufacturing) is used to produce them. Computers in Home: To view encyclopedia information, movies, games, animation, online services, e- mails, downloading file, online shopping, e-banking. Computers at Play: It enables us to play games with them. CP Notes Unit I Page 1

2 They can face instructions differently from each user, animate important concepts and user interactivity to involve users in the learning process. Computers in education: Education software has become a major influence at all levels from elementary schools to universities. Computer in Training: To save money and improve performance, many organizations are using computer based training to train the people. Computers in Entertainment: To create special effects in movies, animation, 3D, etc., Used to edit films during the production process. Computers in the Arts: 3D stereograms allow us to see 3D object hidden inside a single image. Computers in Science and Engineering: Speed: Accuracy Diligence: Satellites are commonly used with the help of computers. Numerous applications in the area of science. In medical technology, physicians are using information technology to understand the human body and to diagnose the disorders. Characteristics of computer: Computer process data at an extremely fast rate. (ie) millions of instruction per second. A computer can perform a huge task in few seconds, but normal human being may takes days or even years to complete. The speed of a computer is calculated in MHz-one million instructions per second. A powerful computer can perform billions of operations in one second. The level of accuracy depends on the instructions and the type of machine being used. The errors in computing are due to human rather than to technological weakness. The computer is capable of doing only what it is instructed to do, faulty instruction for data processing may lead to faulty results. This is known as GIGO (Garbage In Garbage Out). CP Notes Unit I Page 2

3 Reliability: Computer is a machine. It does not suffer from the human tiredness and lack of connection. It performs four million calculations, then the last four-million th calculation with the same accuracy and speed as the first calculation. Reliability is the measurement of performance of computer, which is, measured against some predetermined standard for operation without any failure. The reliability of computer is that, at hardware level, it does not require any human intervention between its processing operations. Computers have built-in diagnostic capabilities, which help in continuous monitoring of the system. Storage capability: Versatility Computer can store large amount of data and can recall the required information almost instantaneously. The main memory of the computer is relatively small and it can hold only a certain amount of information. The data is stored on secondary storage devices, (ie) Magnetic tape or disks. Small section of the data can be accessed quickly and brought into the storage devices, whenever required for processing. Computers are versatile in nature. They can perform multiple tasks simultaneously. Ex. At one moment it can be used to draft a letter, another moment it can be used to play music and in between, one can print a document. Resource sharing: The initial stage of development computer used to be isolated machines. But today computers have the capability to connect with each other. The sharing of costly resources like printer is possible. Apart from device sharing, data and information can also be shared among groups of computer. Generation of computer First generation ( ) (vacuum tubes) The first generation computers are vacuum tubes/thermionic valve based machines. These computers used vacuum tubes for circuitry and magnetic drums for memory. Magnetic drum is a metal cylinder coated with magnetic iron-oxide material. Data and programs stored in magnetic drums. Input-> punched cards and paper tape. Output-> printouts. CP Notes Unit I Page 3

4 It is relied on binary coded language to perform operations and it able to solve only one problem at a time Each machine was fed with different binary codes and hence difficult to program. Drawback: lack of versatility and speed. Characteristics: These computer based on vacuum tube technology. This is the fastest computing device at that time. These computers are very large and required a lot of space for installation. Since thousand of vacuum tubes used, they generated a large amount of heat. So air conditioning was essential. It is non-portable and very slow equipments. They lacked in versatility and speed. They are very expensive to operate and used a large amount of electricity. These machines are unreliable and prone to frequent hardware failures. Since machine language was used, So difficult to program and use. Each individual component hat to be assembled manually. Second generation ( )(transistors) The second generation computer used transistors, which were superior to vacuum tubes. It is made up of semiconductor material like germanium and silicon. It had three leads and performed electrical functions such as voltage, current or power amplification with low power requirements Primary memory->magnetic cores Secondary memory->magnetic disks Input->punched card. Output->printouts The major development of this generation includes the progress from machine language to assembly language. Assembly language->mnemonic code. Ex: ADD for addition MULT for multiplication CP Notes Unit I Page 4

5 Ex: PDP-8, IBM 1401, IBM Characteristics: These machines were based on transistor technology These were smaller as compared to the first generation computers The computation time of these computers was reduced to microseconds from milliseconds. These were more reliable and less prone to hardware failure. It is portable and generated less amount of heat. Assembly language was used to program computers It is also need air conditioning. Manual assembly of individual components into a functioning unit was still required. Third generation ( s) (Integrated Circuits) The development of integrated circuit(ic) is the third generation computers. It consists of single chip with many components such as transistors and resistors fabricated on it. IC replaced several individually wired transistors. This development made computers smaller in size, reliable and efficient. Input->keyboards Output->monitor Interface->Operating system This allowed the device to run many different applications at one time. Ex: NCR 395, B6500 Characteristics: These computers based on integrated circuit technology. The computational time is reduced from microseconds to nanoseconds. It is easily portable and more reliable than the second generation. These devices consumed less power and generated less heat. In some cases, air conditioning was still required. The size of these computers was smaller as compared to previous computers. Since hardware rarely failed, the maintenance cost was quite low. Extensive use of high-level language became possible. Manual assembling of individual components was not required, so it reduced the large requirement of labor and cost. Commercial production became easier and cheaper. CP Notes Unit I Page 5

6 Fourth generation (1970s- Till date) (microprocessors) This is an extension of third generation technology. The technology of this generation was still based on the integrated circuit; these have been made readily available to us because of the development of the microprocessor. A microprocessor is built onto a single piece of silicon, known as chip. It is 0.5 cm alongside and no more than 0.05 cm thick. Large Scale Integration (LSI) and Very Large Scale Integration (VLSI) technology used in this generation. LSI technology allowed thousands of transistors to be constructed on one small slice of silicon materiel. VLSI allowed hundreds of thousands of component on to a single chip. Ultra- Large Scale Integration (ULSI) increased that number into millions. This computers become smaller and cheaper the ever before. Fourth generation computers became more powerful, compact, reliable and affordable. The significant of this computer it could be linked together to form network. Ex: Apple II, Altair 8800, CRAY-1. Characteristics: These computers are microprocessor based system. These computers are very small. It is the cheapest among all the other generation. They are portable and quite reliable. These machines generate negligible amount of heat, hence they do not require air conditioning. Hardware failure is negligible, so minimum maintenance is required. The production cost is very low. GUI and pointing devices enable users to learn to use the computer quickly. Interconnection of computer leads to better communication and resource sharing. Fifth generation (present and beyond) (Artificial Intelligence) The process of developing fifth generation of computers is still in the development stage. CP Notes Unit I Page 6

7 The expert system concept is already in use. The expert system is defined as a computer information system that attempts to mimic the thought process and reasoning of experts in specific areas. Three characteristics can be identified with the fifth generation, Mega chips: This generation computer will use Super Large Scale Integration (SLSI) chips, as a result is the production of microprocessor having millions of electronic components on a single chip. In order to store instruction and information this generation computer requires a great amount of storage capacity. Mega chips may enable the computer to approximate the memory capacity of the human mind. Parallel processing: Computer access and execute only one instruction at a time is called serial processing Computer using parallel processing access several instructions at once and work on them at the same time through use of multiple central processing units. Artificial Intelligence: It refers to a series of related technology that to simulate and reproduce human behavior, including thinking, speaking and reasoning. Classification of computers: Classifications of computer Micro Computers Mini Computers Mainframe Computers Super Computers Desktop computers Laptop Hand held Computer Micro Computers: CP Notes Unit I Page 7

8 It is a small, low cost digital computer which usually consists of a microprocessor, a storage unit, an input channel and an output channel, all of which may be on one chip inserted into one chip inserted into several boards. In addition a power supply and connecting cables, appropriate peripherals, an operating system and other software programs can provide a complete micro computer system. Micro computer generally the smallest of the computer family. Ex IBM-PC, Pentium 100, Apple. Desktop computer: It is otherwise called as personal computer. This is the most common type of micro computer. It is typically consist of a system unit, a display monitor, a keyboard, internal hard disk storage and other peripheral devices. It is less expensive for the individuals or the small business. PC manufacturers-> APPLE, IBM, and DELL. Laptop: A laptop is portable computer that is a user can carry it around. Laptop computer resembles a notebook, so it is also called a notebook. Laptops are small computers enclosing all the basic features of normal desktop computers. The main advantage of this computer is that one can use this computer anywhere and at anytime, especially when one is travelling. These computers do not need any external power supply, as a rechargeable battery is completely self contained in them. These computers are expensive as compared to desktop computers. Hand held computers: It is also called Personal Digital Assistant (PDA). It is a computer that can conveniently be stored in a pocket and used while the user is holding it. PDAs are essentially small portable computers and are slightly bigger than the common calculators. In PDA, user generally uses a pen or electronic stylus, instead of a keyboard for input and the monitor is very small and is the only apparent form of output. CP Notes Unit I Page 8

9 These computers can be easily fitted on the palm, they are also known as palmtop computers. Hand held computers usually have no disk drives, rather they use small card to store programs and data. It has limited memory and is less powerful as compared to desktop computers. Ex. Apple Newton, Casio Cassiopeia, Franklin ebook Man. Mini Computers: The mini computer is a small digital computer whose process and storage capacity is lesser than that of a mainframe, but more than that of micro computer. Speed of processing data is in between that of a mainframe and a micro computer. It is about the size of two drawer filing cabinet. It is used as desktop device that is often connected to a mainframe in order to perform the auxiliary operations. It is also called as mid-range computer. It is capable of supporting from 4 to 200 simultaneous users. It serves as a centralized storehouse for a cluster of workstations or as a network server. Mini computer are usually multi user systems, so these are used in interactive applications, in industries, research organizations, colleges and universities. These are also used for real time control and engineering design work. Ex. IBM, VAX Mainframe computer: Mainframe is an ultra-high performance computer made for high volume, processor intensive computer. It consists of a high end computer processor, with related peripheral devices, capable of supporting large volumes of data processing, high performance online transaction processing systems and extensive data storage and retrieval. It is able to process and store more data than a mini computer and for more than a micro computer. It is designed to perform at a faster rate than a mini computer and at even more faster rate than a micro computer. Main frames can usually execute many programs simultaneously at a high speed. CP Notes Unit I Page 9

10 Mainframe allows its user to maintain large information storage at a centralized location and be able to access and process this data from different computers located at different locations. Ex. VAX 8000, CDC Super computer: Super computer are the special purpose machines, which are specially designed to maximize the number of FLOPS (Floating Point Operation Per Seconds) If any computer below one gigaflop/sec is not a considered a super computer. Super computer has the highest processing speed at a given time for solving scientific and engineering problems. It contains a number of CPUs that operate in parallel to make it faster. Its processing speed lies in the range of ,000 MFLOPS (million of FLOPS). A super computer can process a great deal of information and make extensive calculation very quickly. It is the fastest, costliest and the most powerful computer available today. Super computer are used to solve multi variant mathematical problem of existent physical process, such as aerodynamics, metrology and plasma physics. A super computer has limited broad-spectrum use because of its price tag and limited market. Ex. CRAY-3, Cyber 205, PARAM. Basic Computer Organization A computer is an information processing machine which consists of a number of interrelated components that work together with the aim of converting data into information. To attain information, data is entered through input devices. This data is processed using the central processing unit and then the processed data displayed to the user using various output devices. All these parts are referred to as hardware of the computer. CP Notes Unit I Page 10

11 Central Processing Unit Registers Input Unit Output Unit Control Unit Arithmetic / logic Unit Data flow Instruction flow Input Devices: Input devices are electromechanical devices that allow the user to feed information into the computer for analysis, storage and to give commands to the central processing unit (CPU). Data and instructions are entered into the memory of a computer through input device. It captures information and translates it into a form that can be processed by the CPU. Computer can accept input in two ways. -> Manual -> Direct In manual data entry, the user enters the data into the computer by hand. Ex. Keyboard and Mouse. In direct entry, information is fed into the computer automatically from a source document. Input device are, Keyboard CP Notes Unit I Page 11

12 Mouse Joystick Scanners. Central Processing Unit: The central processing unit referred to as the brain of a computer. It converts data into meaningful information. It is a highly complex, extensive set of electronic circuitry, which executes stored program instructions. It controls all internal and external devices, performs arithmetic and logic operations and operates only on binary data (0s and 1s). It also controls the usage of main memory to store data and instruction,and control the sequence of operations CPU consists of three main subsystems, Arithmetic/logic unit (ALU) Control Unit (CU) Registers. These three subsystems work together to provide operational capabilities to the computer. Arithmetic/logic unit (ALU) It contains the electronic circuitry that executes all the arithmetic and logical operations on the data. The data required to perform the arithmetic and logic functions are inputs from the designated registers. ALU contains two units, Arithmetic Unit Arithmetic unit Logic Unit It contains the circuitry that is responsible for performing the actual computing and carrying out the arithmetic calculation, such as addition, subtraction, multiplication and division. It can perform the operations at very high speed. CP Notes Unit I Page 12

13 Logic Unit: The logic unit enables the CPU to perform logical operations based on the instructions provide it. The operations are logical comparison between data items. This unit can compare numbers, letters, or special character. Logical operations of logic unit can test for three conditions. Control Unit: ->equal to condition -> Less than condition -> Greater than condition This unit checks the correctness of sequence of operations. It fetches program instruction from primary storage unit, interprets them, and ensures correct execution of the program. It also controls the input/output devices and directs the overall functioning of the Registers: other units of the computer. Registers are special purpose, high speed temporary memory units that hold various types of information such as data, instructions, addresses, and the intermediate results of calculation. It holds the information that the CPU is currently working on. Output devices: Humans communicate with the computer through input devices, the computer can communicate with human beings using output devices. The outputs, which can be easily understood and used by human beings, are in the form of hard copy and soft copy. The physical form of output is known as hard copy. The electronic version of an output, which is usually resides in computer memory and/or on disk is known as soft copy. Output devices: Monitor. Printer. CP Notes Unit I Page 13

14 Memory: Plotters. Audio response. CPU handles the processing of data and after processing, presents the results with the help of output devices. Computer requires memory to process data and store output. Memory refers to the electronic holding place for instruction and data. Classify the memory into two categories, Primary memory-> to handle the data Secondary memory-> to store the output. Primary memory: It is also known as main memory, store data and instructions for processing Logically, it is an integral component of CPU but physically, it is a separate part placed on the computer motherboard. It is further classified into Random Access Memory (RAM) and Read Only Memory (ROM). Secondary memory: It is known as auxiliary memory or external memory. It is used for storing instruction and data, since main memory is temporary and limited in size. This memory is least expensive and has much larger storage capacity than primary memory. Instructions and data stored on secondary storage devices are permanent in nature. It can be removed only if the user wants or if the device is destroyed. Number system Introduction: A number is required for counting or to express of some quantity. It consists of a group of symbols called digits, which are arranged in a definite manner. There can be many ways in which the digits can be arranged. The way of arranging the digits is called as number system. The decimal number system has 10 digits (0 9) CP Notes Unit I Page 14

15 The binary number system has 2 digits (0 and 1) The octal number system has 8 digits (0 7) The hexadecimal number system has 16 digits (0 9, A F). The number of digits in a system called radix or base. The decimal number system -> radix 10 (or) base 10 The binary number system -> radix 2 (or) base 2 The octal number system -> radix 8 (or) base 8 The hexadecimal number system -> radix 16 (or) base 16 The number systems are basically two types: Non-positional number system Positional number system Non-positional number system: Human beings counted the number using their fingers. When twenty fingers were not adequate, stones or sticks were used to indicate values This method of counting uses the non-positional number system or additive approach. The symbols of this system as follows, I for 1 II for 2 III for 3 IIII for 4 Disadvantage of this system is difficult to perform arithmetic operations. Positional number system: Ex: The most widely used number system is positional number system. The positional number uses few symbols called digits. Symbol specifies different values depending on the position they occupy in the number. CP Notes Unit I Page 15

16 The decimal number * * * * * *10-2 Position 1000 th 100 th 10 th unit 1/10 th 1/100 th Decimal number system: The number system that is most commonly used is the decimal number system. In this number system the base or radix 10 and there are altogether ten numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. A number in a radix system would be written as follow, a n,a n-1, a n-2, a n-3,.. a 0, a -1, a -2,. a -m can be written as a n r n + a n-1 r n-1 + a n-2 r n-2 + a n-3 r n-3 +. a 0 r 0 + a -1 r -1 + a -2 r a -m r -m In this representation a n is called the Most Significant Digit (MSD) of the number and a -m is called the Least Significant Digits (LSD). Binary Number System: Almost all digital computers and systems are based on binary number system. Binary means two, the binary system uses only two digits 0 s and 1 s. The base or radix of binary system is 2 because it contains only two numbers. In binary number the right most bit is called Least Significant Bit (LSB) and left most bit is called Most Significant Bit (MSB). The weights assigned to bits in the system are power of 2. Purpose for using binary system: Every computer stores numbers, letters and other character in a coded form. As stated every character in storage is represented by a sequence of 0 s and 1 s. These two digits can be arranged in various combinations to represent all the numbers, letters and symbols that can be incorporated into the computer. The computer has been designed to use binary numbers, because of the following reasons: The circuits in computer have to handle by two binary digits or bits rather than decimal numbers. CP Notes Unit I Page 16

17 The computer only identifies signals in the form of digital pulses, which represents either high or low voltage. Everything that can be done with decimal number can also be done using binary number. Octal Number System: The number system with base or radix digit 8 is known as octal number system. There are only eight digits (i.e.) 0, 1, 2, 3, 4, 5, 6, 7 In this system the largest single digit is 7. Each position in this number system represents a power of the base 8. Hexadecimal Number System: Hexadecimal number system is one of the most popular computing systems and is extensively used in microprocessor work. It has a base of 16 and this requires 16 distinct symbols to represents the number. The base 16 suggest choices of 16 single character digit or symbols. The first 10 digits are digits of decimal system (0 to 9) and the remaining 6 digits are denoted by (A to F) representing decimal value (10 to 15). A=10, B=11, C=12, D=13, E=14, F=15. The largest size digit is F which is one less than the base. Since number (0 to 9) and alphabets (A to F) are used to represent the digits in hexadecimal number system, it is also called the called the alphanumeric number systems. Conversion of Number Systems: Conversion of Other number system to Decimal: Binary to Decimal Octal to Decimal Hexadecimal to Decimal Other base numbers to Decimal Binary to Decimal Convert the binary number to decimal number. CP Notes Unit I Page 17

18 =1* * * * * *2 0. 1* * *2-3 =1*32 + 0*16 + 0*8 + 1*4 + 1*2 + 1*1. 1* * *0.125 = = Binary Decimal Octal to Decimal Convert the Octal number 37 8 to decimal number. =3* *8 0. 3* *8-2 =3*8 + 7*1. 3* * = = Octal Decimal Hexadecimal to Decimal Convert the Hexadecimal number E6C4 16 to decimal number. =E* * C* *16 0 =14* * *16 + 4*1 = = Hexadecimal Decimal E6C Other base numbers to Decimal Convert the base-4 number system to decimal number. =1* * * * *4 0 CP Notes Unit I Page 18

19 =1* *64 + 1*16 + 0*4 + 1*1 = = Base-4 Decimal Convert the base-6 number system to decimal number =2* * * *6 0 =2* *36 + 4*6 + 0*1 = = Base-6 Decimal Conversion of Other number system to Binary: Decimal to Binary Octal to Binary Hexadecimal to Binary Other base to Binary Decimal to Binary Convert the Decimal number to Binary number. Step1: Remainder Step2: 2 39 Carry * 2 = * 2 = * 2 = CP Notes Unit I Page 19

20 Decimal Binary Octal to Binary: Convert the octal number to binary number. Each octal digit is converted to its equivalent binary Octal Binary Hexadecimal to Binary: Convert the hexadecimal number 8FAC.BFC 16 to Binary number. Each hexadecimal number is converted to its equivalent binary. 8 F A C. B F C Hexadecimal Binary 8FAC.BFC Other base to Binary: Convert the Base-6 number system to Binary. Step1: Convert the Base-6 number system into decimal system. =2* * * *6 0 =2* *36 + 4*6 + 0*1 = = Base-6 Decimal Step2: Convert Decimal number into Binary Number. CP Notes Unit I Page 20

21 Remainder Base-6 Binary Conversion of Other number system to Octal: Decimal to Octal Binary to Octal Hexadecimal to Octal Other base to Octal Decimal to Octal: Convert the decimal number to Octal number. Step1: 8 31 Remainder 3 7 Step2: Carry * 8 = * 2 = Decimal Octal Binary to Octal: Convert the binary number to Octal number. CP Notes Unit I Page 21

22 Binary Octal Hexadecimal to Octal: Convert the Hexadecimal number CBAED 16 to Octal number. Step1: Convert Hexadecimal to Binary C B A E D Step2: Convert binary to Octal Hexadecimal Octal CBAED Other base to Octal: Convert the base-4 number system to Octal number Step1: Convert Base-4 to decimal =2* * * *4 0 =2*64 + 3*16 + 0*4 + 2*1 = = Step2: Convert Decimal to Octal. Remainder CP Notes Unit I Page 22

23 Base-4 Octal Conversion of Other number system to Hexadecimal number system: Decimal to Hexadecimal Binary to Hexadecimal Octal to Hexadecimal Other base to Hexadecimal Decimal to Hexadecimal: Convert the decimal number to hexadecimal number. Step1: Remainder A Step2: Carry * 16 = * 16 = F.0016 * 16 = * 16 = Decimal Hexadecimal A.2F 16 Binary to Hexadecimal: Convert the Binary number to hexadecimal number A 9. 2 C Binary Hexadecimal A9.2C 16 Octal to Hexadecimal: Convert the Octal number to Hexadecimal number. CP Notes Unit I Page 23

24 Step1: Convert Octal to Binary Number Step2: Convert binary to Hexadecimal number C B A E D Octal Hexadecimal CBAED 16 Other base to Hexadecimal: Convert the base-6 number system to hexadecimal number Step1: Convert base-6 to decimal = 4* * *6 0 =4*36 + 5*6 + 4*1 = = Step2: Convert Decimal to Hexadecimal Remainder B Hints: Other base system to Hexadecimal Other base system to Binary Other base system to Octal Binary to Decimal Octal to Decimal Step1: Convert decimal Step2: Decimal to any one of the base System a n r n + a n-1 r n-1 + a 0 r 0 + a -1 r a -m r -m Using this formula CP Notes Unit I Page 24

25 Hexadecimal to Decimal Decimal to any other base number system r base (or) radix n bit Position 1) Using Remainder Method Remainder Binary to Hexadecimal Binary to Octal Octal to Hexadecimal r Decimal Quotient Remainder 2) Fraction Carry.Decimal Value * r =ans. Decimal Value * r =ans Direct Conversion using 8421(Split 4 bits) Direct Conversion using 421(Split 3 bits) Step1: Convert Octal to Binary. Step2: Convert Binary to Hexadecimal. NEED FOR LOGICAL ANALYSIS AND THINKING ALGORITHM: Algorithms are one of the most basic tools that are used to develop the problem solving logic. Algorithm is defined as a finite sequence of explicit instructions that, when provided with a set of input values produces an output then terminates. Definition: A sequence of instructions designed in such a way that, if the instructions are executed in the specified sequence, the desired results will be obtained. In algorithm, after a finite number of steps, solution of the problem is achieved. Algorithms can have steps that repeat or require decisions until the task is completed. Different algorithms may accomplish the same task with a different set of instructions, in more or less the time, space and efforts. Example to determine the largest number out of three number A, B and C Algorithm: Step1: start the program. Step2: Read three numbers A, B and C. Step3: Find the largest number between A and B, and store it in MAX_AB. Step4: Find the largest number between MAX_AB and C, and store it in MAX. Step5: Display MAX. Step6: Stop the program. CP Notes Unit I Page 25

26 There is a time and space complexity associated with each algorithm. Time complexity specifies the amount of time required by an algorithm for performing the desired task. Space complexity specifies the amount of memory space required by an algorithm for performing the desired task. The algorithms that take less time and require less memory space is the best one. Characteristics of an algorithm: The instructions must be in an ordered form. The instructions must be simple and concise. They must not be ambiguous. There must be an instruction (condition) for program termination. The repetitive programming constructs must have an exit condition. Otherwise the program might run infinitely. The algorithm must completely and definitely solve the given problem statement. Qualities of a good algorithm: It uses the most efficient logic to solve the given problem statement. It uses minimal system memory for its execution. It is able to generate the most accurate results for a wide range if input set. It is easy to implement in the form of a program. It is designed with standard conventions so that others able to easily modify it while adding additional functionality. FLOWCHART: An algorithm is a pictorial representation of an algorithm in which the steps are drawn in the form of different shapes of boxes and the logical flow is indicated by interconnecting arrows. The box represents operations. The arrows represent the sequence in which the operations are implemented. the program. The primary purpose of the flowchart is to help the programmer in understanding the logic of The flowchart drawn according to defined rules and using standard flowchart symbols prescribed by American National Standard Institute (ANSI). The various symbols used in a flowchart are as follows. CP Notes Unit I Page 26

27 The various symbols used in a flowchart are as follows. Guidelines for preparing flowcharts: Flowchart should be clear, neat and easy to follow. Flowchart must have a logical start and finish. Flow lines: Flow lines are used to connect symbols. These lines indicate the sequence of steps and the direction of flow of control. Terminal: This symbol is used to represent the beginning (start), the termination (stop), or halt (pause) in the program logic. Input/ output: It represents information entering or leaving the system, such as user inputs and output. Processing: Process symbol is used for representing arithmetic and data movement instructions. It can be representing a single step or an entire subprocess with in a larger process. Decision: Decision symbols denote a decision to be made. The program should continue along one of the two routes. This symbol has one entry and two exit paths. The path chosen depends on whether the answer to a question is yes or no Connector: Connector symbol is used to join different flow lines. In drawing a proper flowchart, all necessary requirements should be listed in logical order. Only one flow line should come out from a process symbol. Only one flow line should enter a decision and two or more flow lines may leave the decision symbol. Only one flow line is used with a terminal symbol. Within standard symbol, write briefly. If necessary, use the annotation symbol to describe data or process more clearly. For complex flowchart, connector symbols are used to reduce the number of flow lines. Intersection of flow line should be avoided. Benefits of flowcharts: It helps to clarify how things are currently working and how they could be improved. CP Notes Unit I Page 27

28 It helps in finding the key elements of a process by drawing clear line between the end of one process and the start of next one. It helps in revealing redundant or misplaced steps. It makes the logic very clear by the pictorial representation of the task. It is the better way of communicating the logic of the system. It helps in the effective analysis of the problem. The flowcharts act as a guide or blue print during the analysis and program development phase. Flowchart helps to detect errors in the program. It serves as a good program documentation tool. Limitations of flowchart: Flowchart can be used only for basic concept of the program but cannot be used for programming purpose. Pseudocode: For large program, flow chart continue for next page and it is hard to follow and complex. Cost is very high for larger program. It is difficult to modify the complex flowchart. No updating of flowchart can be done. Pseudocode is made up of two words pseudo and code Pseudo imitation / false Code instructions written in a programming language. It is not a real programming code, but it models and may even look like programming code. It is a generic way of describing an algorithm without using any specific programming language related notations. Pseudocode is an outline of a program, written in a form that can be easily converted into real programming statements. It uses plain English statement rather than symbols, to represents the process of a computer program. It is also known as PDL (program design language). Pseudocode instructions are written in normal English but in a structured way. Pseudocode strikes a fine balance between English and a programming language. CP Notes Unit I Page 28

29 If an algorithm is written in English it needs high level description. If an algorithm is written in code the programmer has to invest a lot of time in determining the algorithm. The goal of writing pseudocode is to provide a high level description of an algorithm, which facilities analysis and eventual coding, but suppresses many of the detail that are insignificant. Pseudocode keywords: Input: READ, OBTAIN, GET and PROMPT Output: PRINT, DISPLAY and SHOW Compute: COMPUTE, CALCULATE, DETERMINE Initialize: SET and INITIALISE Add one: INCREMENT Pseudocode is detailed yet readable; it can be inspected by the team of designers and programmers in this way to ensure that actual programming is likely to match design specification. It is the better to catch errors at the pseudocode stage rather than correcting them in later stage. Once the pseudocode is accepted, it is transformed into actual program code using the vocabulary and syntax of the chosen programming language. Pseudocode guidelines: Statements should be written in simple English and should be programming language independent. Pseudocodes only describe the logic plan to develop a program, it is not programming. Steps must be understandable, and when the steps are followed, they must produce a solution to the specified problem. If the pseudocode is difficult for a person to read or translate into code, then detail is wrong. Pseudocode should be concise. Each instruction should be written in a separate line and each statement in pseudocode should express just one action for the computer. Capitalize keywords such as READ, PRINT and so on Each set of instructions is written from top to bottom, with only one entry and one exit. It should allow for easy transition from design to coding in programming language. CP Notes Unit I Page 29

30 Benefits of Pseudocode: Pseudocode provides a simple method of developing program logic. It allows the programmer to focus on the steps required to solve a program rather than on how to use the computer language. Pseudocode is language independent; it can be used by most programmers. It allows the developer to express the design in plain natural language. It is easier to develop a program from a pseudocode than with a flowchart. Programmers do not have to link about syntax. They simply have to concentrate on the underlying logic. It is easy to translate pseudocode into a programming language, which is accomplished by less experienced programmers. The use of words and phrases in pseudocode, which are in line with basic computer operations, simplifies from the pseudocode algorithm to a specific programming language. Pseudocode is compact and does not tend to run over many pages. It s simple structure and readability makes it easier to modify. Limitations of Pseudocode: It does not provide visual representation of the program s logic. There are no accepted standards for writing pseudocodes. Programmers use their own style of writing pseudocode. Pseudocode cannot be compiled nor executed, and there is no real formatting or syntax rules. It is simply one step, an important one, in producing the final code CP Notes Unit I Page 30