C Tutorials

1.1 The C Language

C is programming language developed at AT & T’s Bell Laboratories of USA in 1972. It was designed and written by a man named Dennis Ritchie.

Before C, languages like PL/I, ALGOL etc were used which were replaced by C, because its simple reliable and easy to use.

Okay now lets see how was C developed, what Dennis Ritchie did was, he inherited the features of B ( Language developed by Ken Thompson at AT&T’s Bell Labs ) andBPCL ( Language developed by Martin Richards at Cambridge University )

1.1.1 C – A Middle Level Language

Basically all programming languages are divided into 2 parts

A.) High Level Languages ( Problem oriented languages )

These languages are designed to give a better programming efficiency, i.e. faster program development.

Ex of such languages : FORTRAN, BASIC, PASCAL etc.

B.) Low Level Languages ( Machine Oriented Languages )

These languages are designed to give a better machine efficiency, i.e. faster program execution.

Ex of such languages : Assembly languages and Machine languages.

Now you must be thinking when there are two types of category one High another Low how is C a Middle Level Language.

Answer to this question is that C is designed to have both relatively good programming efficiency (as compared to Machine oriented languages) and a relatively good machine efficiency (as compared to Problem oriented languages)

So it’s a Middle level language.

In short C can do work of both High Level Language and Low Level Language.

*************

1.2 Getting started with C

Whenever we start to learn any language we must first learn about the alphabets or characters used in that language then we combine those alphabets to form a word which are in turn combined to form sentences and sentences to paragraphs and so on.

So in C also we will instead of learning straight away how to write programs we MUST know what are the characters, symbols, numbers used in C, then we have to learn how to using these characters, symbols and numbers we can create constants, variables, keywords are created so that finally we can use all of them to combine and form an instruction cause “A group of instruction would be combined later on to form a program.”

1.2.1 Constants, Variables and Keywords

As we read before the alphabets, numbers and special symbols when properly combined form constants, variables and keywords. Let us see what are ‘constants’ and ‘variables’ in C.

Constant :

It is a quantity that doesn’t change. This quantity can be stored at a location in the memory of computer.

Variable :

It can be considered as a name given to a location in memory where this constant is stored. Also the contents of the variable can change during program execution.

Lets see an example to understand

a=5

Here a “variable” ‘a’ is assigned a “constant” value of ‘5’

1.2.2 Types of Constants

We can divide C constants in two main categories

a.) Primary Constants

b.) Secondary Constants

Right now we will stick to Primary Constants only namely :

• Integer Constants

• Real Constants

• Character Constants

1.2.2.1 Rules for constructing Integer Constants

Integer constants are used to represent whole numbers.

Following are the rules that apply for constructing Integer constants in C :

• An integer constant must have at least one digit.

• It must not have a decimal point.

• It could be either be positive or negative.

• If no sign precedes an integer constant it is assumed to be positive.

• No commas or blanks are allowed within an integer constant.

• Allowable range for integer constants is -32768 to 32767

Examples :

4

109

-2353

-9111

1.2.2.2 Rules for constructing Real Constants

Real constants are used to represent floating point numbers or real numbers.

Real constants can be written in two forms, (a) Fractional Form and (b) Exponential Form.

A.) Following are the rules that apply for constructing Real Constants in Fractional Form :

• A real constant must have at least one digit.

• It must have a decimal point.

• It could be either positive or negative.

• Default sign is positive.

• No commas or blanks are allowed with a real constant.

Examples :

+323.212

460.0

-23.121

-85.323

B.) Following are the rules that apply for constructing Real Constants in Exponential Form :

• The mantissa part and exponential part should be separated by letter “e”.

• The mantissa part may have a positive part or a negative part.

• Default sign of mantissa part is positive.

• The exponent must have at least one digit which must be positive or negative integer. Default sign is positive.

• Range of real constants expressed in exponential form is -3.4e38 to 3.4e38

Examples :

+3.4e5

-0.2e+3

-3.2e1

5.1e9

1.2.2.3 Rules for constructing character constants.

Following are set of rules that apply for constructing character constant

• A character constant is either a single alphabet, a single digit or a single special symbol enclosed within single quotes.

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

Examples :

‘a’

‘I’

‘%’

‘=’

‘7’

1.2.3 Type of C Variables
As explained earlier, a variable is named location in memory in which different constants are stored. These constants can be any of the constants explained above. Also the contents of variable can be change during program execution. The type of a variable depends upon the type of constant it stores.

There are some rules that apply for constructing variable names in C

• A variable name is any combination of 1 to 8 alphabets, digits or underscores. Some compliers allow variable names whose length could be upto 40 characters. Still it would be safer to stick to the rule of 8 characters.

• The first character in the variable name must be alphabet.

• No commas or blanks are allowed within a variable name.

• No special symbol other than an underscore can be used in variable name.

Valid Examples :

ro_hit

p_4_f

Invalid Examples :

$dollar

4fun

_hello

not ok

1.2.4 C Character Set

The set of characters that may appear is valid C program is called as Character set for C. The set includes some graphic and non graphic characters.
Graphic characters contain alphabets, digits, and special symbols.

Check them here :

Alphabets

A…..Z

a…….z

Digits

0…..9

Special Characters :

,  comma

.  period

;  semicolon

:  colon

^  caret

*  asterisk

=  equal

>  greater than

(  left parenthesis

[  left bracket

}  right brace

_ underscore

$  dollar

%  percent

&  ampersand

+   plus

)   right parenthesis

]  right bracket

‘  accent grave

Now graphic characters contain white spaces. These are now printing characters. Which instructs the computer to take a certain action. They are called escape sequences consisting of a back slash (\) followed by a letter.

Let’s see

\a audible beep

\f form feed

\t horizontal tab

\v vertical tab

\b back space

\r carriage return

\n new line

\” qoutes

1.2.5 C Keywords

Keywords are the words whose meaning has already been explained to C compiler (or in a broad sense to the computer). 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. Some C compilers allow u to construct variable names which exactly resembles the keywords. However, it would be safer not to mix up the variable names and the keywords. The keywords are also called ‘Reserved words’.

There are 32 keywords available in C.

They are :

auto

break

case

char

const

continue

default

do

far

for

double

else

enum

extern

float

if

int

long

near

register

return

short

signed

static

struct

switch

typedef

union

unsigned

void

while

We will discuss all these keywords later.

*************

1.3 First C Program

After starting with basics of C language, now its time to do a simple C program. This program will give you a basic idea of how to write a C program. This is just a simple program we will discuss complex programs later.

Here is your first program :

/* This is a simple program */
#include<stdio.h>
#include<conio.h>
void main ()
{
clrscr();
printf(“Welcome to C\n\nTuts By P4F”);
getch();
}

Result :

Welcome to C

Tuts By P4F

Now let us closely examine each part of the program

1.) /* This is a simple program */

This is a comment. We use comments to enter a remark in a program, it can be used anywhere in a program cause contents of comments are ignored by compiler, so to explain or describe the operation of a program to any one who is reading the program we use comments.

Few important points :

Multiline comments are enclosed in /* */

For example

/* This
is a
comment */

if our comment is in single line we can use // also

For example

// This is a comment

2.) #include<stdio.h>
#include<conio.h>

These are pre-processor directives. We will study about them later. Till than use these two in all your programs.

3.) void main ()

All C program start execution with the main () function about which we will discuss later.
And writing void before main () indicates that there is no return type specified to the main function, so while compiling the compiler will understand that there is no return type, finally you need not return anything, we could have used int, char, float in place of void according to our program, you will understand everything clearly later as u proceed.

4.) {

This character(opening curly brace) indicates the start of the main ()’s body. All the code written must be contained within the body of the main() function.

5.) clrscr();

We use this function in the beginning in order to clear screen before proceeding to the program.
Suppose we did a program before running this program so if we don’t use clrscr(); compiler will show result of last program with our current program, so in order to erase all other previous results we use clrscr();

6.) printf(“Welcome to C\n\nTuts By P4F”);

printf function is a function used to print on to the screen.
Here in this case result will be

Welcome to C

Tuts By P4F

Note :

1. We used 2 “\n\n” so that means there will be 2 new lines between Welcome to C and Tuts By P4F.
2. Any message to be printed on screen should be included within double quotes as shown.

7.) ;

Remember each statement of C should be terminated using semicolon “;”

8.) getch();

We use getch(); function in order to hold the screen till we press any key after execution of the program, otherwise program will run and output will be shown on screen for few seconds only.

9.) }

Finally, the closing curly brace “}” is used to close the body of the main() function.

*************

Session Summary

• C is a middle level language.

• A constant is a quantity that doesn’t change. This quantity can be stored at a location in the memory of the computer.

• A variable can be considered as a name given to the location in memory where this constant is stored. Also the contents of the variable can change during program execution.

• Character set in C is divided into graphic and non graphic characters.

• Graphic characters include all valid ASCII characters.

• Non graphic characters contain white spaces and are called escape sequences.

• Comments are used to enter a remark in program

*************

Thats end of our 1st tutorial, thanks for reading it, if you have any doubts please feel free to ask we will surely reply to your questions.

Team P4F

- Rohit Nambiar