Programming in C �Unit 1

ES-101/102

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MODULE 1

LECTURE NOTE-1

A BEGINNER’S GUIDE

INTRODUCTION TO COMPUTERS

Any programming language is implemented on a computer. Right form its inception, to the present day, all computer system (irrespective of their shape & size) perform the following 5 basic operations. It converts the raw input data into information, which is useful to the users.

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• Inputting: It is the process of entering data & instructions to the computer system.
• Storing: The data & instructions are stored for either initial or additional processing, as & when required.
• Processing: It requires performing arithmetic or logical operation on the saved data to convert it into useful information.
• Outputting: It is the process of producing the output data to the end user.
• Controlling: The above operations have to be directed in a particular sequence to be completed.

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Based on these 5 operations, we can sketch the block diagram of a computer.

Fig 1: Block Diagram of a Computer

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Fig 1: Block Diagram of a Computer

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BVCOE New Delhi Subject: Programming In C , Instructor: Anu Yadav

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• Input Unit: We need to first enter the data & instruction in the computer system, before any computation begins. This task is accomplished by the input devices. (Eg: keyboard, mouse, scanner, digital camera etc). This device is responsible for linking the system with the external environment. The data accepted is in a human readable form. The input device converts it into a computer readable form.

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• Storage Unit: The data & instruction that are entered have to be stored in the computer. Similarly, the end results & the intermediate results also have to be stored somewhere before being passed to the output unit. The storage unit provides solution to all these issues. This storage unit is designed to save the initial data, the intermediate result & the final result. This storage unit has 2 units: Primary storage & Secondary storage.

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Primary Storage: The primary storage, also called as the main memory, holds the data when the computer is currently on. As soon as the system is switched off or restarted, the information held in primary storage disappears (i.e. it is volatile in nature). Moreover, the primary storage normally has a limited storage capacity, because it is very expensive as it is made up of semiconductor devices.

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Secondary Storage: The secondary storage, also called as the auxiliary storage, handles the storage limitation & the volatile nature of the primary memory. It can retain information even when the system is off. It is basically used for holding the program instructions & data on which the computer is not working on currently, but needs to process them later.

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• Central Processing Unit: Together the Control Unit & the Arithmetic Logic Unit are called as the Central Processing Unit (CPU). The CPU is the brain of the computer. Like in humans, the major decisions are taken by the brain itself & other body parts function as directed by the brain. Similarly in a computer system, all the major calculations & comparisons are made inside the CPU. The CPU is responsible for activating & controlling the operation of other units of the computer system.

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Arithmetic Logic Unit: The actual execution of the instructions (arithmetic or logical operations) takes place over here. The data & instructions stored in the primary storage are transferred as & when required. No processing is done in the primary storage. Intermediate results that are generated in ALU are temporarily transferred back to the primary storage, until needed later. Hence, data may move from the primary storage to ALU & back again to storage, many times, before the processing is done.

Control Unit: This unit controls the operations of all parts of the computer but does not carry out any actual data processing.It is responsible for the transfer of data and instructions among other units of the computer.It manages and coordinates all the

units of the system.It also communicates with Input/Output devices for transfer of data or results from the storage units.

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• Output Unit: The job of an output unit is just the opposite of an input unit. It accepts the results produced by the computer in coded form. It converts these coded results to human readable form. Finally, it displays the converted results to the outside world with the help of output devices ( Eg :monitors, printers, projectors etc..).

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So when we talk about a computer, we actually mean 2 things:

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• Hardware- This hardware is responsible for all the physical work of the computer.
• Software- This software commands the hardware what to do & how to do it.

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Together, the hardware & software form the computer system.

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This software is further classified as system software & application software.

System Software- System software are a set of programs, responsible for running the computer, controlling various operations of computer systems and management of computer resources. They act as an interface between the hardware of the computer & the application software. E.g.: Operating System

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Application Software- Application software is a set of programs designed to solve a particular problem for users. It allows the end user to do something besides simply running the hardware. E.g.: Web Browser, Gaming Software, etc.

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LECTURE NOTE-2

INTRODUCTION TO PROGRAMMING

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A language that is acceptable to a computer system is called a computer language or programming language and the process of creating a sequence of instructions in such a language is called programming or coding. A program is a set of instructions, written to perform a specific task by the computer. A set of large program is called software. To develop software, one must have knowledge of a programming language.

Before moving on to any programming language, it is important to know about the various types of languages used by the computer. Let us first know what the basic requirements of the programmers were & what difficulties they faced while programming in that language.

COMPUTER LANGUAGES

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Languages are a means of communication. Normally people interact with each other through a language. On the same pattern, communication with computers is carried out through a language. This language is understood both by the user and the machine. Just as every language like English, Hindi has its own grammatical rules; every computer language is also bounded by rules known as syntax of that language. The user is bound by that syntax while communicating with the computer system.

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Computer languages are broadly classified as:

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• Low Level Language: The term low level highlights the fact that it is closer to a language which the machine understands.

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The low level languages are classified as:

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• Machine Language: This is the language (in the form of 0’s and 1’s, called binary numbers) understood directly by the computer. It is machine dependent. It is difficult to learn and even more difficult to write programs.

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• Assembly Language: This is the language where the machine codes comprising of 0’sand 1’s are substituted by symbolic codes (called mnemonics) to improve their understanding. It is the first step to improve programming structure. Assembly language programming is simpler and less time consuming than machine level programming, it is easier to locate and correct errors in assembly language than in machine language programs. It is also machine dependent. Programmers must have knowledge of the machine on which the program will run.

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• Linker: A linker or link editor is a computer program that takes one or more object files generated by a compiler and combines them into a single executable file, library file, or another object file.

LECTURE NOTE -3

INTRODUCTION TO C

Brief History of C

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• The C programming language is a structure oriented programming language, developed at Bell Laboratories in 1972 by Dennis Ritchie.
• C programming language features were derived from an earlier language called “B”

(Basic Combined Programming Language – BCPL)

• C language was invented for implementing UNIX operating system.
• In 1978, Dennis Ritchie and Brian Kernighan published the first edition “The C Programming Language” and is commonly known as K&R C.
• In 1983, the American National Standards Institute (ANSI) established a committee to provide a modern, comprehensive definition of C. The resulting definition, the ANSI standard, or “ANSI C”, was completed late 1988.
• Many of C’s ideas & principles were derived from the earlier language B, thereby naming this new language “C”.

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Taxonomy of C Language

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WHY IS C POPULAR

• It is reliable, simple and easy to use.
• C is a small, block-structured programming language.
• C is a portable language, which means that C programs written on one system can be run on other systems with little or no modification.
• C has one of the largest assortments of operators, such as those used for calculations and data comparisons.
• Although the programmer has more freedom with data storage, the languages do not check data type accuracy for the programmer.

WHY TO STUDY C

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• By the early 1980s, C was already a dominant language in the minicomputer world of Unix systems. Since then, it has spread to personal computers (microcomputers) and to mainframes.
• Many software houses use C as the preferred language for producing word processing

programs, spreadsheets, compilers, and other products.

• C is an extremely flexible language—particularly if it is to be used to write operating systems.
• Unlike most other languages that have only four or five levels of precedence, C has 15.

CHARECTERESTICS OF A C PROGRAM

• Middle level language.

• Small size – has only 32 keywords
• Extensive use of function calls- enables the end user to add their own functions to the C library.
• Supports loose typing – a character can be treated as an integer & vice versa.
• Structured language

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• Low level (Bit Wise) programming readily available
• Pointer implementation - extensive use of pointers for memory, array, structures and functions.
• It has high-level constructs.
• It can handle low-level activities.
• It produces efficient programs.
• It can be compiled on a variety of computers.

USES

The C programming language is used for developing system applications that forms a major portion of operating systems such as Windows, UNIX and Linux. Below are some examples of C being used:

• Database systems
• Graphics packages
• Word processors
• Spreadsheets
• Operating system development
• Compilers and Assemblers
• Network drivers
• Interpreters

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STRUCTURE OF A C PROGRAM

The structure of a C program is a protocol (rules) to the programmer, which he has to follow while writing a C program. The general basic structure of C program is shown in the figure below.

Based on this structure, we can sketch a C program.

Example:

/* This program accepts a number & displays it to the user*/

#include <stdio.h> void main(void)

{ int number;

printf( "Please enter a number: " ); scanf( "%d", &number );

printf( "You entered %d", number ); return 0;}

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Stepwise explanation:

#include

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• The part of the compiler which actually gets your program from the source file is called the preprocessor.
• #include <stdio.h>
• #include is a pre-processor directive. It is not really part of our program, but instead it is an instruction to the compiler to make it do something. It tells the C compiler to include the contents of a file (in this case the system file called stdio.h).
• The compiler knows it is a system file, and therefore must be looked for in a special place, by the fact that the filename is enclosed in <> characters

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<stdio.h>

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• stdio.h is the name of the standard library definition file for all STanDard Input and Output functions.
• Your program will almost certainly want to send information to the screen and read things from the keyboard, and stdio.h is the name of the file in which the functions that we want to use are defined.
• The function we want to use is called printf. The actual code of printf will be tied in later by the linker.
• The ".h" portion of the filename is the language extension, which denotes an include file.

void

• This literally means that this means nothing. In this case, it is referring to the function whose name follows.
• Void tells to C compiler that a given entity has no meaning, and produces no error.

main

• In this particular example, the only function in the program is called main.
• A C program is typically made up of large number of functions. Each of these is given a name by the programmer and they refer to each other as the program runs.
• C regards the name main as a special case and will run this function first i.e. the program execution starts from main.

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(void)

• This is a pair of brackets enclosing the keyword void.
• It tells the compiler that the function main has no parameters.
• A parameter to a function gives the function something to work on.

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{ (Brace)

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• This is a brace (or curly bracket). As the name implies, braces come in packs of two - for every open brace there must be a matching close one.
• Braces allow us to group pieces of program together, often called a block.
• A block can contain the declaration of variable used within it, followed by a sequence of program statements.
• In this case the braces enclose the working parts of the function main.

; (semicolon)

• The semicolon marks the end of the list of variable names, and also the end of that declaration statement.
• All statements in C programs are separated by ";" (semicolon) characters.
• The ";" character is actually very important. It tells the compiler where a given statement ends.
• If the compiler does not find one of these characters where it expects to see one, then it will produce an error.

scanf

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• In other programming languages, the printing and reading functions are a part of the language.
• In C this is not the case; instead they are defined as standard functions which are part of the language specification, but are not a part of the language itself.
• The standard input/output library contains a number of functions for formatted data transfer; the two we are going to use are scanf (scan formatted) and printf (print formatted).

printf

• The printf function is the opposite of scanf.
• It takes text and values from within the program and sends it out onto the screen.
• Just like scanf, it is common to all versions of C and just like scanf, it is described in the system file stdio.h.
• The first parameter to a printf is the format string, which contains text, value descriptions and formatting instructions.

FILES USED IN A C PROGRAM

• Source File- This file contains the source code of the program. The file extension of any c file is .c. The file contains C source code that defines the main function & maybe other functions.

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• Header File- A header file is a file with extension .h which contains the C function declarations and macro definitions and to be shared between several source files.
• Object File- An object file is a file containing object code, with an extension .o, meaning

relocatable format machine code that is usually not directly executable. Object files are produced by an assembler, compiler, or other language translator, and used as input to the linker, which in turn typically generates an executable or library by combining parts of object files.

• Executable File- The binary executable file is generated by the linker. The linker links the various object files to produce a binary file that can be directly executed.

COMPLIATION & EXECUTION OF A C PROGRAM

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ELEMENTS OF C

Every language has some basic elements & grammatical rules. Before starting with programming, we should be acquainted with the basic elements that build the language.

Character Set

Communicating with a computer involves speaking the language the computer understands. In C, various characters have been given to communicate.

Character set in C consists of;

Keywords

Keywords are the words whose meaning has already been explained to the C compiler. The keywords cannot be used as variable names because if we do so we are trying to assign a new meaning to the keyword, which is not allowed by the computer.

There are only 32 keywords available in C. Below figure gives a list of these keywords for your ready reference.

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Identifier

In the programming language C, an identifier is a combination of alphanumeric characters, the first being a letter of the alphabet or an underline, and the remaining being any letter of the alphabet, any numeric digit, or the underline.

Two rules must be kept in mind when naming identifiers.

1. The case of alphabetic characters is significant. Using "INDEX" for a variable is not the same as using "index" and neither of them is the same as using "InDeX" for a variable. All three refer to different variables.
2. As C is defined, up to 32 significant characters can be used and will be considered significant by most compilers. If more than 32 are used, they will be ignored by the

compiler.

Data Type

In the C programming language, data types refer to a domain of allowed values & the operations that can be performed on those values. The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted. There are 4 fundamental data types in C, which are- char, int, float &, double. Char is used to store any single character; int is used to store any integer value, float is used to store any single precision floating point number & double is used to store any double precision floating point number. We can use 2 qualifiers with these basic types to get more types.

There are 2 types of qualifiers-

Sign qualifier- signed & unsigned Size qualifier- short & long

The data types in C can be classified as follows:

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Constants

A constant is an entity that doesn’t change whereas a variable is an entity that may change.

C constants can be divided into two major categories:

• Primary Constants
• Secondary Constants

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Here our only focus is on primary constant. For constructing these different types of constants certain rules have been laid down.

Rules for Constructing Integer Constants:

An integer constant must have at least one digit.

1. It must not have a decimal point.
2. It can be either positive or negative.

3. If no sign precedes an integer constant it is assumed to be positive.
4. No commas or blanks are allowed within an integer constant.
5. The allowable range for integer constants is -32768to 32767. Ex.: 426, +782,-8000, -7605

Rules for Constructing Real Constants:

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Real constants are often called Floating Point constants. The real constants could be written in two forms—Fractional form and Exponential form.

Rules for constructing real constants expressed in fractional form:

1. A real constant must have at least one digit.
2. It must have a decimal point.
3. It could be either positive or negative.
4. Default sign is positive.
5. No commas or blanks are allowed within a real constant. Ex. +325.34, 426.0, -32.76, -48.5792

Rules for constructing real constants expressed in exponential form:

1. The mantissa part and the exponential part should be separated by a letter e.
2. The mantissa part may have a positive or negative sign.
3. Default sign of mantissa part is positive.
4. The exponent must have at least one digit, which must be a positive or negative integer. Default sign is positive.
5. Range of real constants expressed in exponential form is -3.4e38 to 3.4e38. Ex. +3.2e-5, 4.1e8, -0.2e+3, -3.2e-5

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Rules for Constructing Character Constants:

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1. A character constant is a single alphabet, a single digit or a single special symbol enclosed within single inverted commas.

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• The maximum length of a character constant can be 1 character.

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Ex.: ‘M’, ‘6’, ‘+’

VARIABLES

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Variables are names that are used to store values. It can take different values but one at a time. A data type is associated with each variable & it decides what values the variable can take. When you decide your program needs another variable, you simply declare (or define) a new variable and C makes sure you get it. You declare all C variables at the top of whatever blocks of code need them. Variable declaration requires that you inform C of the variable's name and data type. Syntax – datatype variablename;

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Eg:

int page_no;

char grade; float salary; long y;

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Declaring Variables:

There are two places where you can declare a variable:

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After the opening brace of a block of code (usually at the top of a function)

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Before a function name (such as before main() in the program) Consider various examples:

Suppose you had to keep track of a person's first, middle, and last initials. Because an initial is obviously a character, it would be prudent to declare three character variables to hold the three initials. In C, you could do that with the following statement:

main()

{

char first, middle, last;

// Rest of program follows

}

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2. main()

{ char first; char middle; char last;

// Rest of program follows

}

• Initialization of Variables

When a variable is declared, it contains undefined value commonly known as garbage value. If we want we can assign some initial value to the variables during the declaration itself. This is called initialization of the variable.

Eg- int pageno=10;

char grade=’A’;

float salary= 20000.50;

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Expressions

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An expression consists of a combination of operators, operands, variables & function calls. An expression can be arithmetic, logical or relational. Here are some expressions:

a+b – arithmetic operation a>b- relational operation a

== b - logical operation func (a,b) – function call

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a*(b + c/d)/20 q = 5*2 x =

++q % 3

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q > 3

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Compound Statements (Blocks)

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A compound statement is two or more statements grouped together by enclosing them in braces; it is also called a block. The following while statement contains an example:

while (years < 100)

{

wisdom = wisdom * 1.05; printf("%d %d\n", years, wisdom); years = years + 1;

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}

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If any variable is declared inside the block then it can be declared only at the beginning of the block. The variables that are declared inside a block can be used only within the block.

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INPUT-OUTPUT IN C

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When we are saying Input that means we feed some data into program. This can be given in the form of file or from command line. C programming language provides a set of built-in functions to read given input and feed it to the program as per requirement.

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When we are saying Output that means to display some data on screen, printer or in any file. C programming language provides a set of built-in functions to output the data on the computer screen.

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Functions printf() and scanf() are the most commonly used to display out and take input respectively. Let us consider an example:

#include <stdio.h> int main()

{

//This is needed to run printf() function.

printf("C Programming"); //displays the content inside quotation return 0;

}

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Output:

C Programming

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Explanation:

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• Every program starts from main() function.
• printf() is a library function to display output which only works if #include<stdio.h>is included at the beginning.
• Here, stdio.h is a header file (standard input output header file) and #include is command to paste the code from the header file when necessary. When compiler encounters printf()function and doesn't find stdio.h header file, compiler shows error.
• return 0; indicates the successful execution of the program.

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Input- Output of integers in C

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#include<stdio.h> int main()

{

int c=5;

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printf("Number=%d",c); return 0;

}

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Output

Number=5

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Inside quotation of printf() there, is a conversion format string "%d" (for integer). If this conversion format string matches with remaining argument, i.e, c in this case, value of c is displayed.

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#include<stdio.h> int main()

{ int c;

printf("Enter a number\n"); scanf("%d",&c); printf("Number=%d",c); return 0;

}

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Output

Enter a number 4

Number=4

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The scanf() function is used to take input from user. In this program, the user is asked an input and value is stored in variable c. Note the '&' sign before c. &c denotes the address of c and value is stored in that address.

Input- Output of floats in C

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#include <stdio.h> int main()

{

float a;

printf("Enter value: "); scanf("%f",&a);

printf("Value=%f",a); //%f is used for floats instead of %d return 0;

}

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return 0;

}

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Output:

Enter character:

g

103

When, 'g' is entered, ASCII value 103 is stored instead of g.

You can display character if you know ASCII code only. This is shown by following example.

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#include <stdio.h> int main()

{

int var1=69;

printf("Character of ASCII value 69: %c",var1); return 0;

}

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Output

Character of ASCII value 69: E

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The ASCII value of 'A' is 65, 'B' is 66 and so on to 'Z' is 90. Similarly ASCII value of 'a' is 97, 'b' is 98 and so on to 'z' is 122.

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OPERATORS

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C language is rich in built-in operators and provides the following types of operators:

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• Arithmetic Operators
• Relational Operators
• Logical Operators
• Bitwise Operators
• Assignment Operators
• Increment and decrement operators
• Conditional operators
• Misc Operators

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Arithmetic operator:

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These are used to perform mathematical calculations like addition, subtraction, multiplication, division and modulus.

Following table shows all the arithmetic operators supported by C language. Assume variable A holds 10 and variable B holds 20 then:

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Relational Operators:

These operators are used to compare the value of two variables.

Following table shows all the relational operators supported by C language. Assume variable A holds 10 and variable B holds 20, then:

Logical Operators:

These operators are used to perform logical operations on the given two variables.

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Following table shows all the logical operators supported by C language. Assume variable A holds 1 and variable B holds 0, then:

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Bitwise Operators

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Bitwise operator works on bits and performs bit-by-bit operation. Bitwise operators are used in bit level programming. These operators can operate upon int and char but not on float and double.

Showbits( ) function can be used to display the binary representation of any integer or character value.

Bit wise operators in C language are; & (bitwise AND), | (bitwise OR), ~ (bitwise OR), ^ (XOR),

<< (left shift) and >> (right shift).

The truth tables for &, |, and ^ are as follows:

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The Bitwise operators supported by C language are explained in the following table. Assume variable A holds 60 (00111100) and variable B holds 13 (00001101), then:

Assignment Operators:

In C programs, values for the variables are assigned using assignment operators. There are following assignment operators supported by C language:

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INCREMENT AND DECREMENT OPERATOR

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In C, ++ and – are called increment and decrement operators respectively. Both of these operators are unary operators, i.e, used on single operand. ++ adds 1 to operand and – subtracts 1 to operand respectively. For example:

Let a=5 and b=10 a++; //a becomes 6 a--; //a becomes 5

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++a; //a becomes 6

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--a; //a becomes 5

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When i++ is used as prefix(like: ++var), ++var will increment the value of var and then return it but, if ++ is used as postfix(like: var++), operator will return the value of operand first and then only increment it. This can be demonstrated by an example:

#include <stdio.h> int main()

{

int c=2,d=2;

printf(“%d\n”,c++); //this statement displays 2 then, only c incremented by 1 to 3.

Printf(“%d”,++c); //this statement increments 1 to c then, only c is displayed.

Return 0;

}

Output

2

4

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Conditional Operators (? :)

Conditional operators are used in decision making in C programming, i.e, executes different statements according to test condition whether it is either true or false.

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Syntax of conditional operators;

conditional_expression?expression1:expression2

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If the test condition is true (that is, if its value is non-zero), expression1 is returned and if false expression2 is returned.

Let us understand this with the help of a few examples:

int x, y ;

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scanf ( “%d”, &x ) ;

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y = ( x> 5 ? 3 : 4 ) ;

This statement will store 3 in y if x is greater than 5, otherwise it will store 4 in y. The equivalent if statement will be,

if ( x > 5 )

y = 3 ;

else

y = 4 ;

Misc Operators:

There are few other operators supported by c language.

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Operators Precedence in C

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator.

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For example x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.

Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

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