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| Chapter 1 | Introduction to Programming Concepts - Part 1 |
Input, Process, and Output
You might have noticed computers being used at airline reservation counters, shops, restaurants, and various other locations. At each of these places, a user enters some values in the computer and the computer generates an output, which is either displayed on the computer screen or printed on paper. Let us consider the example of an airline reservation counter. When you want a seat reserved on a particular flight, you provide information about your requirements such as destination, date and time of your departure, and the class in which booking is required. The clerk at the reservation counter enters this information into a computer. Details regarding the availability of tickets are then displayed on the screen.
Let us see what are the phases involved and the process followed for each of the task.Phases
To understand what happens when you enter some values in the computer, let us break the
entire set of activities into separate phases. In the first phase, flight requirements are
keyed into the computer. This phase is called the
input
phase. The flight requirement
information is then processed to determine whether or not seats are available on the
particular flight. This phase is known as the
process
phase. Once the processing is
complete, the result is displayed on the computer screen, indicating the status of seat
availability. This phase is called the
output
phase.
I-P-O Cycle
The cycle of activities performed by a computer also follows the
Input-Process-Output
cycle or the I-P-O cycle. A computer consists of several components such as a keyboard,
mouse, monitor, printer and a central processing unit. Each component participates in
either one of the input, process, or output phases. For example, the keyboard and mouse
are used for input. The central processing unit and the memory inside the system unit of
the computer are used for processing. The monitor and printer are used for output.
Programs and Programming Language
Computer follows an I-P-O cycle. It needs set of instructions called program to specify
the input required, process to be followed, and the output required.
Program is written in a specific language called Programming Language, so that computer
can understand the instructions.
Let us understand Program and Programming Language more in detail.
Programs
How does a computer know what are the steps to be followed to process reservation
requests? How does it manage to calculate your shopping bills at the local store? How
does it generate your report card at school? Is it an all-knowing machine? Do you have to
buy a different computer for each of these above-mentioned activities? The answer to the
last two questions is ‘No’. It is not an all-knowing machine and you do not require a
separate computer for each of these activities.
Then, how does a computer function? A computer is designed to accept input, process it,
and generate output. However, it has to be provided with a set of instructions that state the
following:
- The kind of input that will be provided. For example, in the case of reservation requests, flight date, flight time, class, and destination will be some of the inputs.
- The kind of output expected. For example, the seat availability status.
- The processing that needs to be done. For example, accepting the values, checking for availability of seats, and displaying results.
A set of instructions to perform a particular job is called a program . Therefore, for each job that you want the computer to perform, you require a separate program. Instructions in a program can be:
- Sequential : Instructions that are executed one after the other.
- Decision Making : Instructions that evaluate an expression (relation or condition) first and then, depending upon whether the value of the expression is 'true' (non-zero) or 'false' (zero), it transfers the control to a particular statement.
- Iterative : Instructions that are executed repeatedly, depending on the value of an expression (relation or condition).
Any real-life problem will consist of a number of small jobs. Therefore, to solve a real-life problem, you have a number of programs that together form an application. For example, a payroll application for processing employee compensation details and generating paychecks and associated reports might have two programs:
- Program to generate paychecks
- Program to print reports.
Programming Languages
A computer is made up of a number of electronic components. An electronic component
can be either in an on state or an off state. Therefore, the components of a computer are
represented as a combination of on and off states. The on state is represented by ‘1’ and
the off state by ‘0’. This implies that a computer can understand only 0s and 1s.
Therefore, any instruction given to a computer must be a sequence of 0s and 1s.
A sequence of 0s and 1s can be used to describe any physical operation that the computer
performs. Therefore, a computer system uses a number system that consists of only two
digits, 0 and 1. This number system is known as the binary number system.
The language that the computer understands is called the
machine language
. For example,
the machine language for a particular computer could have the following instruction set:
It is doubtful if you would be comfortable writing a program in machine language. It is
certainly difficult for anybody to remember instructions in the form of 0s and 1s.
Therefore, we use high-level programming languages to write programs. A high-level
programming language consists of a set of instructions, which are represented using simple English words. So, when you want the computer to display the output on the
screen, you type the instruction ‘WRITE ON SCREEN’ and not ‘00100000’.
There are many high-level programming languages available, such as C, C++, and Java.
Each language has its own advantages. You need to evaluate the problem at hand before
deciding on the programming language to use.
All languages have a vocabulary, which is a list of words that have a specific meaning in
that language. Languages also have their own grammar rules, which state the rules for
combining words to form sentences. This is what ensures that whatever is spoken in a
particular language is interpreted similarly by all people who understand the language.
Simi larly, programming languages also have a vocabulary, whi ch is referred to as the set
of
keywords
of that language, and a grammar, which is referred to as the
syntax.
As stated earlier, a program written in any programming language is a set of logically
related instructions. These instructions have two parts, as shown in the following figure:
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| Format of a Programming Language Instruction |
The two parts of a programming language instruction are:
- Operation code (opcode) : This part instructs a computer about the operation to be performed.
- Operand : This part instructs the computer about the location of the data on which the operation specified by the opcode is to be performed.
For example, in the instruction Add A and B,
Add
is the opcode and
A and B
are
operands.
Compilers
Can computers directly interpret the instructions written in any programming language?
No, they cannot. Then, how do you ensure that a computer executes the instructions from
a program, as intended? What would you do if you got hold of a recipe for a delicious
dish written in a foreign language that you do not understand? You would get it translated
into English or any other language you understand to be able to prepare the dish.
Similarly, you need a translator to convert the instructions written in a programming
language into machine language.
A compiler is a special program that processes the statements written in a particular
programming language and converts them into machine language at one go. Like
everything else in the computer, the compiler also follows the I-P -O cycle. It takes the
programming language instructions as input. It then processes these instructions to
convert them to machine language. These instructions can then be executed by the
computer. This process of conversion is called compilation. For each programming
language, there is a different compiler available. For example, for compiling a program
written in the C language, you require a C compiler, and likewise, for a Java program, you
require a Java compiler.
Continue Read - Introduction to Programming Concepts - Part 2
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