Lecture Note: 1
Introduction to C
C is a programming language developed at AT & T’s Bell Laboratories of USA
in 1972. It was designed and written by a man named Dennis Ritchie. In the late
seventies C began to replace the more familiar languages of that time like PL/I,
ALGOL, etc
ANSI C standard emerged in the early 1980s, this book was split into two
titles: The original was still called Programming in C, and the title that covered
ANSI C was called Programming in ANSI C. This was done because it took
several years for the compiler vendors to release their ANSI C compilers and for
them to become ubiquitous. It was initially designed for programming UNIX
operating system. Now the software tool as well as the C compiler is written in C.
Major parts of popular operating systems like Windows, UNIX, Linux is still
written in C. This is because even today when it comes to performance (speed of
execution) nothing beats C. Moreover, if one is to extend the operating system to
work with new devices one needs to write device driver programs. These
programs are exclusively written in C. C seems so popular is because it is
reliable,
simple and easy to use. often heard today is – “C has been already superceded
by languages like C++, C# and Java.
Program
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There is a close analogy between learning English language and learning C
language. The classical method of learning English is to first learn the alphabets
used in the language, then learn to combine these alphabets to form words, which
in turn are combined to form sentences and sentences are combined to form
paragraphs. Learning C is similar and easier. Instead of straight-away learning how
to write programs, we must first know what alphabets, numbers and special
symbols are used in C, then how using them constants, variables and keywords are
constructed, and finally how are these combined to form an instruction. A group
of instructions would be combined later on to form a program. So
a computer program is just a collection of the instructions necessary to solve a
specific problem. The basic operations of a computer system form what is known
as the computer’s instruction set. And the approach or method that is used to solve
the problem is known as an algorithm.
So for as programming language concern these are of two types.
1) Low level language
2) High level language
Low level language:
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Low level languages are machine level and assembly level language. In
machine level language computer only understand digital numbers i.e. in the form
of 0 and 1. So, instruction given to the computer is in the form binary digit,
which
is difficult to implement instruction in binary code. This type of program is not
portable, difficult to maintain and also error prone. The assembly language is on
other hand modified version of machine level language. Where instructions are
given in English like word as ADD, SUM, MOV etc. It is easy to write and
understand but not understand by the machine. So the translator used here is
assembler to translate into machine level. Although language is bit easier,
programmer has to know low level details related to low level language. In the
assembly level language the data are stored in the computer register, which varies
for different computer. Hence it is not portable.
High level language:
These languages are machine independent, means it is portable. The language in
this category is Pascal, Cobol, Fortran etc. High level languages are understood by
the machine. So it need to translate by the translator into machine level. A
translator is software which is used to translate high level language as well as
low
level language in to machine level language.
