Skip to main content

C Tokens

Tokens are classified as
  • Keywords
  • Identifiers
  • Operators
  • Constants
  • Special Symbols
Keywords are reserved by the compilers and keywords will not be redefined (means the keywords are not been declared as variable names, etc). There are standard 32 keywords in C compiler, and some compilers uses more keywords based on their specification. Here is the list of 32 keywords
auto break case char
const continue default do
double else enum extern
float for goto if
int long register return
short signed sizeof static
struct switch typedef union
unsigned void volatile while

  1. Identifiers are variable names declared inside the program.
  2. They use alphabets, number, symbols like _ and $
  3. They must begin with  alphabet or _
  4. They are case sensitive i.e Var_name is different from var_name
Some valid identifiers are
john Value r_sie x1
x2 Chennai Sum1 abcd
invalid identifiers
123 % (super) 25th
1st ab-d sum of total

operators are further classified into different categories like
  • Arithmetic operators
+  - for addition   1+3 = 4
-   for subtraction      3 – 2 = 1        
*  for multiplication 4* 2 = 8
/   for Division      4 / 2    = 2
% for modulo  4 % 3 = 1 (when 4 is divided by 3, the remainder is 1)
  • Increment/ Decrement operators
++  increment Ex: a++ or ++a
--  decrement Ex: a—or –a
  • relational Operators
< – less than
> – greater than
<= less than or equal to
>= greater than or equal to
== is equal to
  • logical operators
&&  - Logical AND
||   - Logical OR
!  - Logical NOT
  • bitwise operators
& Bitwise AND
| bitwise OR
^ bitwise XOR
~ one’s complement
<< shift left
>> shift right
  • Conditional Operators
? : Conditional operator
f =(a>b) ?a : b;
if the condition a> b is true then
a is assigned to f and if false then b is assigned to f
the statement can be rewritten as
  • Other Operators
= assignment operator (this is not equality operator, it just assigns the value to some other variable from right to left assignment)
Example: a=b means b is assigned to a
, comma operator (This is to separate the array variables, etc)
sizeof() operator (to find out the various sizes of the entities like int, char, array size, etc)
  • Special symbols
{} This to begin and end any statement, loop in C program
[] This is for specifying the array index (Ex: int a[10];)
()  This is used for functions in C and helpful for grouping arithmetical operations
  • Constants is an entity will never changes it value during the execution of the program
  • They are different from variables

  • Integer constant
Examples are 2, –1, 0, 345, 324, etc
  • float Constant
Examples are 3.0, –2.345, 32.56, 4.65
  • String Constant
“abc”, “Pradeep Kumar”
  • Character constant
‘A’, ‘b’, ‘1’
There are two ways to declare a constant
1st way is to define at the preprocessing level
Example is
#define PI 31.4
2nd way is declare inside the program
const int a=3.14;
const is the keyword to define a constant.

 T S Pradeep Kumar


Popular posts from this blog

Installation of ns2 in Ubuntu 18.04 - NS2 Tutorial # 2

ns2 installation in Ubuntu 18.04

Unlike earlier version of ubuntu, the 18,04 version does not support the direct installation of ns2, because of the latest C/C++ compiler (7.x), but the latest C/C++ compiler supported by ns2 is gcc-4.8. So this post and video tells you about the installation of gcc-4.8 version, then ns2 and then configuration.
Here are the steps, Please follow the video given below for more information.

$] tar zxvf ns-allinone-2.35.tar.gz

$] sudo apt install gcc-4.8 g++-4.8

if you have installed ubuntu just now, you can try these commands also in the beginning

$] sudo apt update
$] sudo apt install build-essential autoconf automake libxmu-dev

$] cd ns-allinone-2.35/ns-2.35
$] gedit
$] gedit linkstate/ls.h

line number 137, change erase to this->erase
$] cd ..
$] ./install

export PATH=$PATH:/home/pradeepkumar/ns-allinone-2.35/bin:/home/pradeepkumar/ns-allinone-2.35/tcl8.5.10/unix:/home/pradeepkumar/ns-allinone-2.35/tk8.5.10/unix

ns3 installation in Ubuntu 16.04

This post serves the installation instructions of ns3 in ubuntu 16.04 version. Some of my students are working in ns3, this post will benefit them in installing ns3.

OS Used: Ubuntu 16.04.4
ns3 version: ns3 version 3.27

The same procedure will be applied for OS like Debian, Linux Mint.

Fresh installation of Ubuntu 16.04 Let you try the fresh installation of ubuntu in your hard disk along with windows.
Installation of ns3 dependencies ns3 needs so many dependencies, developmental libraries, drivers, etc. so install all those
$] sudo apt update  $] sudo apt upgrade
$] sudo apt-get install build-essential autoconf automake libxmu-dev python-pygoocanvas python-pygraphviz cvs mercurial bzr git cmake p7zip-full python-matplotlib python-tk python-dev python-kiwi python-gnome2 python-gnome2-desktop-dev python-rsvg qt4-dev-tools qt4-qmake qt4-qmake qt4-default gnuplot-x11 wireshark
The above command make take some time to download, compile and install it, Be Patient. 
Installing ns3 Download the…

AWK Scripts for NS2 to process data from Trace Files

AWK Scripts are very good in processing the data from the log (trace files) which we get from NS2. If you want to process the trace file manually, here is the detailHere is a sample of trace file from NS2 (However ns2 supports a new type of trace file also), but this post will make you understand the old trace format only.r 0.030085562 _0_ MAC  --- 0 message 32 [0 ffffffff 1 800] ------- [1:255 -1:255 32 0] r 0.030110562 _0_ RTR  --- 0 message 32 [0 ffffffff 1 800] ------- [1:255 -1:255 32 0] s 1.119926192 _0_ RTR  --- 1 message 32 [0 0 0 0] ------- [0:255 -1:255 32 0]
AWK Scripts are very good in processing the data column wise. For example
the first column in the above trace file represents r, s which indicates receive, sent respectively. If we want to trace the entire r and s alone from this trace file we can represent it as $1
$1 represents ACTION
$2 Time
$3 Node ID
$4 Layer
$5 Flags
$6 seqno
$7 type
$8 Size
$14 Energy (if the network nodes includes EnergyModel)To run the awk script in Li…