Unit – 1

Introduction To Programming

1.1 Introduction To Components Of A Computer System (Disks, Memory, Processor,

Where A Program Is Stored And Executed Operating System, Compilers Etc).

Disks:

Generally, a disk is a a round plate on which data can be encoded. There are two basic
types of disks: magnetic disks and optical disks.

Magnetic Disks
In magnetic disks, the data is encoded as microscopic magnetized needles on the disk's
surface. You can record and erase data on a magnetic disk any number of times
Magnetic disks come in a number of different forms:

 Floppy disk: A typical 5¼-inch floppy disk can hold 360K or 1.2MB megabytes.
3½-inch floppies normally store 720K, 1.2MB or 1.44MB of data. Floppy disks or
obsolete today.
 Harddisk :Hard disks can store anywhere from 20MB to more than 1-TB (terabyte).
Hard disks are also from 10 to 100 times faster than floppy disks.
 Removablecartridge : Removable cartridges are hard disks encased in a metal or
plastic cartridge, so you can remove them just like a floppy disk. Removable
cartridges are fast, though usually not as fast as fixed hard disks.

Memory:

A memory is used to store data and instructions. Computer memory is the storage
space in the computer, where data is to be processed and instructions required for
processing are stored. The memory is divided into large number of small parts called
cells. Each location or cell has a unique address, which varies from zero to memory size
minus one.

For example, if the computer has 64k words, then this memory unit has 64 * 1024 =
65536 memory locations. The address of these locations varies from 0 to 65535.

Memory is primarily of three types −

 Cache Memory
  Primary Memory/Main Memory
 Secondary Memory

Cache Memory

Cache memory is a high -speed semiconductor memory which can speed up the CPU.
It acts as a buffer between the CPU and the main memory. It is used to hold those parts
of data and program which are most frequently used by the CPU. The parts of data and
programs are transferred from the disk to cache memory by the operating system,
from where the CPU can access them.

Advantages

The advantages of cache memory are as follows −

 Cache memory is faster than main memory.

 It consumes less access time as compared to main memory.
 It stores the program that can be executed within a short period of time.
 It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows −

 Cache memory has limited capacity.

 It is too expensive.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which the computer is
currently working. It has a limited capacity and data is lost when power is switched off.
It is generally made up of semiconductor device. These memories are not as fast as
registers. The data and instruction required to be processed resides in the main
memory. It is divided into two subcategories RAM and ROM.

Characteristics of Main Memory

 These are semiconductor memories.

 It is known as the main memory.
 Usually volatile memory.
 Data is lost in case power is switched off.
 It is the working memory of the computer.
  Faster than secondary memories.
 A computer cannot run without the primary memory.

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than
the main memory. These are used for storing data/information permanently. CPU
directly does not access these memories, instead they are accessed via input-output
routines. The contents of secondary memories are first transferred to the main memory,
and then the CPU can access it. For example, disk, CD-ROM, DVD, etc.

Characteristics of Secondary Memory

 These are magnetic and optical memories.

 It is known as the backup memory.
 It is a non-volatile memory.
 Data is permanently stored even if power is switched off.
 It is used for storage of data in a computer.
 Computer may run without the secondary memory.
 Slower than primary memories.

Processor:

A processor (CPU) is the logic circuitry that responds to and processes the basic
instructions that drive a computer. The CPU is the main integrated circuitry (IC) chip in a
computer, as it is responsible for interpreting most of computers commands. CPUs will
perform most basic arithmetic, logic, and I/O operations, as well as allocate commands
for other chips and components running in a computer.

The basic elements of a processor include:

 The arithmetic logic unit (ALU), which carries out arithmetic and logic operations
on the operands in instructions.
 The floating -point unit (FPU), also known as a math coprocessor or numeric
coprocessor, a specialized co-processor that manipulates numbers more quickly
than the basic microprocessor circuitry can.
 Registers, which hold instructions and other data. Registers supply operands to the
ALU and store the results of operations.
  L1 and L2 cache memory. Their inclusion in the CPU saves time compared to
having to get data from random access memory (RAM).

CPU Operations

The four primary functions of a processor are fetch, decode, execute and write back.

Fetch- is the operation which receives instructions from program memory from a
systems RAM.

Decode- is where the instruction is converted to understand which other parts of the
CPU are needed to continue the operation. This is performed by the instruction decoder

Execute- is where the operation is performed. Each part of the CPU that is needed is
activated to carry out the instructions.

Program stored and executed operating system:

Whenever you save your program(anything) into a file (any kind of file, say ‘add.c’), it
automatically gets stored in the secondary storage that is the hard disk. The Operating
System’s kernel (kernel’s File management system) does it for you.

When you run program, it is loaded into the main/primary memory of the computer
called RAM (the entire program is transferred to the RAM, by a small program called
the loader (which often comes with the compiler i.e. is a part of the compiler).

The program instructions are executed in the ALU (Arithmetic-Logic Unit) of the CPU (in
its registers like the Accumulator). In order to execute the instructions , the CPU
fetches the values of the variables (say, int a =10; int b =20;) in the program from the
RAM, and stores the results also in the RAM (int sum =30;), which is then sent to the
output buffer stream (stdout) , which prints the results (30) on the computer
console/terminal, the Windows kernel (kernel’s I/O management system) does the
printing .

Compilers:
Compiler is a program that translates source code into object code. The compiler
derives its name from the way it works, looking at the entire piece of source code and
collecting and reorganizing the instructions. Thus, a compiler differs from
an interpreter, which analyses and executes each line of source code in succession,
without looking at the entire program. The advantage of interpreters is that they can
execute a program immediately. Compilers require some time before an executable
program emerges. However, programs produced by compilers run much faster than the
same programs executed by an interpreter.
Every high- level programming language comes with a compiler. In effect, the compiler
is the because it defines which instructions are acceptable.
Because compilers translate source code into object code, which is unique for each type
of computer many compilers are available for the same language.

1.2 Idea Of Algorithm: Steps To Solve Logical And Numerical Problems

An algorithm is the finite set of English statements which are designed to accomplish the
specific task. Study of any algorithm is based on the following four criteria

1. Design of algorithm:This is the first step in the creation of an algorithm. Design of

algorithm includes the problem statement which tell user about the area for which
algorithm is required. After problem statement next important thing required is the
information about available and required resources. The last thing required in design of
algorithm phase is information about the expected output.

2. Validation of algorithm: Once an algorithm is designed , it is necessary to validate it

for several possible input and make sure that algorithm is providing correct output for
every input. This process is known as algorithm validation. The purpose of the validation
is to assure us that this algorithm will work correctly independently of the issues
concerning the programming language it will eventually be written in.

3. Analysis of algorithm: Analysis of algorithms is also called as performance analysis.

This phase refers to the task of determining how much computing time and storage an
algorithm requires. The efficiency is measured in best case, worst case and average
case analysis.

4. Testing of algorithm:This phase is about to testing of a program which coded as per

the algorithm. Testing of such program consists of two phases:

 Debugging: It is the process of executing programs on sample data sets to determine

whether faulty results occur or not and if occur, to correct them.

 Profiling : Profiling or performance measurement is the process of executing a

correct program on data sets and measuring the time and space it takes to
compute the result

Characteristics of an algorithm

 Input: Algorithm must accept zero or more inputs.

 Output: Algorithm must provide at least one quantity.

 Definiteness: Algorithm must consist of clear and unambiguous instruction.

 Finiteness: Algorithm must contain finite set of instruction and algorithm will
terminates after a finite number of steps.

 Effectiveness: Every instruction in algorithm must be very basic and effective.

Uses of algorithm

 Algorithm provide independent layout of the program.

 It is easy to develop the program in any desired language with help of layout.

 Algorithm representation is very easy to understand.

 To design algorithm there is no need of expertise in programming language.

1.3 Representation Of Algorithm: Flowchart/Pseudo Code With Examples. From

Algorithms To Programs

There are three ways to represent an algorithm. Consider the following algorithm of
addition of two numbers

Step 1 : Start

Step 2 :Read a number, say x and y

Step 3 :Add x and y

Step 4 :Display Addition

Step 5 :Stop

1. Flowcharts: A flow chart is a diagrammatic / pictorial representation of an algorithm.

It is the simplest way of representation of algorithm. Initially an algorithm is represented
in the form of flowchart and then flowchart is given to programmer to express it in some
programming language. Logical error detection is very easy in flowchart as it shows the
flow of operations in diagrammatic form. Once flowchart is ready it is very easy to write
a program in terms of statements of a programming language. Following are the
symbols used in designing the flowcharts.

2. Pseudo code: Pseudo code is the combination of English statements with

programming methodology. In pseudo code, there is no restriction of following the
syntax of the programming language. Pseudo codes cannot be compiled. It is just a
previous step of developing a code for given algorithm.

3. Program: In this way of representation, complete algorithm is represented using

some programming language by following the complete syntax of programming
language.

Sr. Name of Symbol Meaning / Purpose

No. Symbol
1. Terminal To indicate START / STOP.
Usually it is the first symbol
 and last symbol used in
program logic.
2. Input / To indicate input / output of
Output Data
Statement
3. Processing To indicate the processing of
Statement instructions.
4. To indicate decision making
and a branch to one or more
Decision alternatives.
Box

5. Flow Lines To indicate the direction of

flow of information.
6. Connector It is used when flowchart
becomes long and need to be
continued. Shows the
continuity of the algorithm on
the next page.

1.4 Source Code

Source code is the list of human-readable instructions that a programmer writes—often

in a word processing program—when he is developing a program. The source code is
run through to turn it in compiler to machine code called as object code.

1.5 Variables (With Data Types) Variables And Memory Locations

Variables are the names you give to computer memory locations which are used to store
values in a computer program.
Here are the following three simple steps −

 Create variables with appropriate names.

 Store your values in those two variables.
 Retrieve and use the stored values from the variables.
When creating a variable, we need to declare the data type it contains.

Programming languages define data types differently.

For example, almost all languages differentiate between ‘integers’ (or whole
numbers, eg 12), ‘non-integers’ (numbers with decimals, eg 0.24), and ‘characters’
(letters of the alphabet or words).

 char – a single 16-bit Unicode character, such as a letter, decimal or punctuation

symbol.

 boolean – can have only two possible values: true (1) or false (0). This data type is
useful in conditional statements.
 byte - has a minimum value of -128 and a maximum value of 127 (inclusive).
 short– has a minimum value of -32,768 and a maximum value of 32,767
 int: – has a minimum value of -2,147,483,648 and a maximum value of 2,147,483,647
(inclusive).
 long – has a minimum value of -9,223,372,036,854,775,808 and a maximum value of
9,223,372,036,854,775,807 (inclusive).
 float – a floating point number with 32-bits of precision
 double – this is a double precision floating point number.

1.6 Type Casting/Type Conversion

Type casting refers to changing variable of one data type into another. The compiler
will automatically change one type of data into another. For instance, if you assign an
integer value to a floating-point variable, the compiler will convert the int to a float.
Casting allows you to make this type conversion explicit, or to force it when it would
not normally happen.

Type conversion in c can be classified into the following two types:

1. Implicit Type Conversion

When the type conversion is performed automatically by the compiler

without programmers intervention, such type of conversion is known as implicit type
conversion or type promotion.
int x;

for(x=97; x<=122; x++)

printf("%c", x); /*Implicit casting from int to char thanks to %c*/

2. Explicit Type Conversion

The type conversion performed by the programmer by posing the data type of the
expression of specific type is known as explicit type conversion. The explicit type
conversion is also known as type casting.

Type casting in c is done in the following form:

(data_type)expression;

where, data_type is any valid c data type, and expression may be constant, variable
or expression.

For example,

int x;

for(x=97; x<=122; x++)

printf("%c", (char)x); /*Explicit casting from int to char*/

The following rules need to be followed while converting the expression from one
type to another to avoid the loss of information:

 All integer types to be converted to float.

 All float types to be converted to double.
 All character types to be converted to integer.

Example
Consider the following code:

int x=7, y=5 ;

float z;

z=x/y; /*Here the value of z is 1*/

If we want to get the exact value of 7/5 then we need explicit casting from int to float:

int x=7, y=5;

float z;

z = (float)x/(float)y; /*Here the value of z is 1.4*/

1.7 Run Time Environment (Static, Dynamic Location)

Stands for "Runtime Environment." As soon as a software program is executed, it is in

a run time state. In this state, the program can send instructions to the computer's
processor and access the computer's memory and other system resources.

When software developers write programs, they need to test them in the runtime
environment. Therefore, software development programs often include an RTE
component that allows the programmer to test the program while it is running. This
allows the program to be run in an environment where the programmer can track
the instructions being processed by the program and debug any errors that may
arise. If the program crashes, the RTE software keeps running and may provide
important information about why the program crashed.

1.8 Storage Classes (Auto, Register, Static, Extern)

A storage class is used to describe the following things:

 The variable scope.

 The location where the variable will be stored.
 The initialized value of a variable.
 A lifetime of a variable.
1.9 Syntax And Logical Errors In Compilation

A syntax error is an error in the source code of a program. Since computer programs
must follow strict syntax to compile correctly, any aspects of the code that do not
conform to the syntax of the programming language will produce a syntax error.

• Spelling mistakes

• Missing out quotes

• Missing out brackets

• Using upper case characters in key words e.g. IF instead of if

• Missing out a colon or semicolon at end of a statement

• Using tokens in the wrong order A logic error (or logical error) is a ‘bug’ or
mistake in a program’s source code that results in incorrect or unexpected
behaviour. It is a type of runtime error that may simply produce the wrong output or
may cause a program to crash while running.

1.10 Object and Executable Code

 

Source code is the C program that you write in your editor and save with a ‘ .C ‘
extension which is un-compiled when written for the first time or whenever a
change is made in it and saved.

Object code is the output of a compiler after it processes the source code. The
object code is usually a machine code, also called a machine language, which can
be understood directly by a specific type of CPU. However, some compilers are
designed to convert source code into an assembly language or some other another
programming language. An assembly language is a human-readable notation using
the mnemonics in the ISA of that particular CPU.

Executable (also called the Binary) is the output of a linker after it processes
the object code. A machine code file can be immediately executable, runnable as
a program , or it might require linking with other object code files for
example libraries to produce a complete executable program.