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Installation of ns3 in Ubuntu | Ubuntu 24.04 | ns-3.42

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


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