C Programming

Jigar Jobanputra

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• C is a general-purpose structured programming language that is powerful, efficient and compact.

• C combines the features of high-level language with elements of the assembler and thus, the close to both man and machine (computer).

• C was developed and implemented at Bell Laboratories in 1972 by Dennis Richie.

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• Important of C or features of C.• It is a robust language whose rich set of built-in function and

operators can be used to write any complex program.• The C compiler combines the capabilities of an assembly language

with the features of a high-level language and therefore it was suited for writing both system software and business packages. In fact, many of compilers available in market are written in C.

• Program written in C are efficient and fast, this is due to variety of data types and powerful operators.

• There are only 32 keywords and its strength lies in its in-built functions. Several standard functions are available which can be used for developing programs.

• C is highly portable, its means that C programs written for one computer can be run on another with little or no modification.

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• C language is well suited structured programming, thus required the user to think of a program in terms of function modules or blocks. Proper collections of these modules make a complete program. This modular structure makes program debugging, testing and maintenance easier.

• C is its ability to extend itself. A c program is basically collection of functions that are supported by the C library. We can continuously add our own function to the c library. Thus with availability of large number of functions, the programming task becomes simple.

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• C Instructions:• Type declaration instructions: used to declare types of variables

used in programs. E.g. int a;• Input/output instructions: used to input data required by program

and information to be output on printer/screen. E.g. printf and scanf.• Arithmetic Instructions: arithmetic instruction done between

constants and variables. Eg. Assignment statement.• Control instructions: To maintain order of execution of different

statements control instruction are used. They are following types:• Unconditional control statement e.g Goto statement.• Decision control statement e.g. IF statement.• Loop control statement e.g For and do statement.• Case control statement .e.g Case statement.

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• Basic structure of C programs:• 1. Documentation section: consists of a set of

comments lines giving the name of program, author and other detail which programmer would like to use later.

• 2. Link section: this section provides instruction to compiler to link function from system library.

• 3. Definition Section: this section defines all symbolic constants.

• 4. Global Declaration section: there are some variables that are used in more than one function. Such variables are called global variables and are declared in global definition section that is out side of all the functions.

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• 5. Main( ) function section: every c program must have one main( ) function section and its divided in to two part one is declaration part and executable part. The declaration part declares all the variables used in executable part. There is at least one statement in executable part. And these two parts appear between opening and closing braces ( { } ). All the statements in the declaration and executable parts end with a semicolon ( ; ).

• 6. Subprogram section: this section contains all the user-defined functions that are called in the main section. User-defined functions are generally placed immediately after the main function, although they may appear in any order.

C Program Characteristics

• Reliability: i.e the program can be depended upon always to do what is supposed to do.

• Integrity: This refers to accuracy of the calculations. It should be clear that all the other program enhancements would be meaningless if the calculations were not carried out correctly.

• Clarity or Readability: It refers to the overall readability of the program, with particular emphasis on its underlying logic. If the program is written clearly, it should be possible for another programmer to follow the logic without undue effort.

• Maintainability: i.e. the program will be easy to change or modify when the need arises.

• Portability: i.e. the program will be transferable to different computer with a minimum of modification.

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• Performance or Efficiency: i.e. the program causes the tasks to be done quickly and efficiently. It also concerned with execution speed and efficient memory utilization this aid reliability, maintainability and portability.

• Storage saving: i.e. the program is not allowed to be unnecessarily long.

• Modularity: Many programs can be decomposed into series of identifiable sub tasks. It is good programming practices to implement each of these subtasks as a separate module. (In Pascal, such module refers as procedures and functions). The use a modular programming structure enhances the accuracy and clarity of a program, and it facilities future for program alterations.

VARIABLES

• A variable is a named data storage location in your computer’s memory.

• By using a variable’s name in your program, you are, in effect, referring to the data stored there.

VARIABLE NAMING CONVENTION

• To use variables in your C programs, you must know ho to create variable names in

• C,variables names must adhere to the following rules:– The name can contain letters, digits, and the underscore

character(_).– The first character of the name must be a letter. The

underscore is also a legal first character, but its use is not recommended.

– Case matters (that is uppercase and lowercase letters). Thus, the names count and Count refer to two different variables.

– C keywords can’t be used as variable names. A keyword is a word that is part of the C language.

Different Programming Language

• There are three different level of programming languages. They are

• (1) Machine languages (low level)• (2) Assembly languages• (3) Procedure Oriented languages (high

level)• (4) Fourth Generation languages (4 GLS)

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• (1) Machine Languages :-• Computers are made of No. of electronic

components and they all are two – state electronic components means they understand only the 0 – (pulse) and 1 (non – pulse).

• Therefore the instruction given to the computer must be written using binary numbers. 1and 0.

• Computers do not understand English or any other language but they only understand or respond to binary numbers (0 and 1). So each computer has its own Machine languages.

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• (2) Assembly Languages :-• As it was very tedious to understand and

remember 0’s representing numerous data and instruction.

• So to resolve this problem mnemonics codes were developed. For example add isused as symbolic code to represent addition. SUB is used for subtraction.

• They are the symbolic representation of certain combination of binary numbers

• for example• S U B

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• Which represents certain actions as computer understand only Machine language instructions a program written in Assembly Language must be translated into Machine languages.

• Before it can be executed this translation if done by another program called assembler. This assembler will translate mnemonic codes into Machine languages.

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• (3) Procedure Oriented Languages• In earlier assembly languages assembler

programs produced only one Machine languages instruction for every assembly languages instruction.

• So to resolve this problem now assembler were introduced. Which can produce several machine level instructions for one assembly language instruction.

• Thus programmer was relieve from the task of writing and instruction for every machine operation performed. These languages contains set of words and symbols and one can write program with the combination of these keywords.

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• These languages are also called high level languages. Basic, Fortran, Pascal and COBOL.

• The most important characteristic of high level languages is that it is machine independent and a program written in high level languages can be run on any computers with different architecture with no modification or very little modification.

WHAT IS LANGUAGE TRANSLATORS?

• As we know that computer understand only the instruction written in the Machine language. Therefore a program written in any other language should be translated to Machine language. For this purpose special programs are available they are called translators or language processors. This special programs accept the user program and check each statement and produces a corresponding set of Machine language instructions. There are two types of Translators.

Compiler

• A Compiler checks the entire program written by user and if it is free from error and mistakes then produces a complete program in Machine language known as object program.

• But if it founds some error in program then it does not execute the single statement of the program.

• So compiler translate whole program in Machine language before it starts execution.

Interpreters

• Interpreters performs the similar job like compiler but in different way. It translates (Interprets) one statement at a time and if it is error – free then executes that statement. This continues till the last statement in the program has been translated and executed.

• Thus Interpreter translates and executes the statement before it goes to next statement. When it founds some error in statement it will immediately stop the execution of the program.

• Since compiler of Interpreter can translate only a particular language for which it is designed one has to use different compiler for different languages.

Difference of Compiler – Interpreter

• Error finding is much easier in Interpreter because it checks and executes each statement at a time. So wherever it fine some error it will stop the execution.

• Where Compiler first check all the statement for error and provide lists of all the errors in the program.

• Interpreter take more time for the execution of a program compared to Compilers because it translates and executes each statement one by one.

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• All programming languages can be divided into two categories:– Problem oriented languages or high

languages – Machine oriented languages or Low Level

Languages

Problem oriented languages or high languages

• Examples of languages falling in this category are FORTRAN, BASIC, Pascal, etc.

• These languages have been designed to give a better programming efficiency, faster program development. Generally these languages have better programming capability but they are less capable to deal with hardware or Hardware related programming.

Machine oriented languages or Low Level Languages

• Examples of languages falling in this category are Assembly language and Machine Language.

• This languages have been designed to give a better machine efficiency i.e. faster program execution.

• Generally these languages have better hardware programming capability but it is very difficult and tedious to do create complex application like and business application or some commercial application