Unit-I Chapter 2 C Tokens: Character set, Identifiers ...

Prepared by Aravinda Kasukurthi, CSE, RVRJCCE

Unit-I Chapter 2

C Tokens: Character set, Identifiers, Keywords, constants, Data types, type qualifiers, Declaration and Initialization of variables.

C Tokens

Token: The smallest individual units in a program are called tokens.

The ‘C’ tokens are classified as:

1. Character set 2. Keywords 3. Identifiers 4. Constants 5. Operators

Character set: Character set consists of

i) alphabet from A-Z or a-z ii) digits from 0-9 iii) Special characters like (,), {,}, [,], <, >, &, $, #, %, ^, !, ?, :, ;, ",', . iv) White space character: blank space v) Escape sequences:

\b backspace \a audible bell \v vertical tab \t horizontal tab \f form feed \r carriage return \” double quotes \’ single quotes \\ back slash

\r is a carriage return character; it tells your terminal emulator to move the cursor at the start of the line. The cursor is the position where the next characters will be rendered. So, printing a \r allows overriding the current line of the terminal emulator.


Example Program: #include<stdio.h> main() { printf("Backspace Character\b"); printf(" Audible Bell\a\n"); printf("Vertical Tab\vDemonstration\n"); printf("Horizental Tab\tDefault 8 spaces\n"); printf("Form feed\fIt is only with Printer\n"); printf("Carriage Return\rmove the cursor at the start of the line\n"); printf("Single Quotes The \"Sun\" rises in the \'east\'\n"); printf("Backslash \\hai\n"); } Output: Backspace Characte Audible Bell Vertical Tab Demonstration Horizental Tab Default 8 spaces Form feed It is only with Printer move the cursor at the start of the line Double quotes and Single Quotes The "Sun" rises in the 'east' Backslash \hai Keywords: Keywords are reserved words. All keywords have fixed meanings. Keywords serve as basic building blocks for program statements. In ‘C’, there are 32 keywords. All keywords must be written in lower case. These 32 keywords are classified into 3 types namely

1. Type related Keywords (16) 2. Storage related Keywords (4) 3. Control flow related Keywords (12)


Type related Keywords:

int short void enum float long struct const char signed union volatile double unsigned typedef sizeof

Storage related keywords:

auto static register extern Control flow related keywords:

if default goto for else case continue while switch break return do

Identifiers: Identifier refers to the names of the variables, functions and arrays.

Rules to name a particular identifier:

1. It must start with either alphabet or underscore. 2. Remaining letters may be alphabet, digit, underscore. 3. Identifier would not allow any special symbol except underscore. 4. An identifier can be of any length while most compilers of ‘C’

language recognize only the first 8 characters. 5. Do not use keywords as an identifier.

Constants: Constants refer to fixed values that do not change during the execution of a program. Constants are 2 types.

1. Numerical constants 2. Non-numerical constants Numerical Constants are 2 types.

i. Integer constants ii. Real constants


Non- Numerical Constants are 2 types. i. Character constants

ii. String or multiple character constants

Integer constants: An integer constant refers to a sequence of digits. There are three types of integers, namely, decimal, octal and hexadecimal.

Decimal integers consist of a set of digits, 0 through 9, preceded by an optional – or + sign.

Valid examples of decimal integer constants are: 321, -789, 0, +77

An octal integer constant consists of any combination of digits from the set 0 through 7, with leading 0.

Some examples of octal integers are 047, 0, 0543, 0655

Hexadecimal integer constant consists of a sequence of digits preceded by 0x or 0X.

They may also include alphabets A through F or a through f. (0 – 9 and A – F or a – f)

Examples of hexadecimal integer constants are: 0X49, 0x8D

Real constants:

Some quantities vary continuously, such as distances, heights, temperatures, prices and so on.

These quantities are represented by numbers containing fractional parts. Such numbers are called real or floating point constants.

A real constant is a sequence of digits with a decimal point. Examples of real constants are:

0.00876, -0.456, 543.78, +247.0 A real number may also be expressed in exponential or scientific

notation. Example is:

The value 289.45 may be written as 2.8945e2 in exponential notation.


General form is:

mantissa e exponent

The mantissa is either a real number expressed in decimal notation or an integer.

The exponent is an integer number with an optional plus or minus sign.

The letter e is either in lowercase or uppercase.

Single Character constants (Character constant):

A single character constant contains a single character (alphabet, digit, special symbol, white space) enclosed within a pair of single quote marks.

Examples are: '1', 'a', ' ','@' Note: Character constants have integer values known as ASCII values. Since each character constant represent an integer value, so character arithmetic is possible. Example Program: #include<stdio.h> main() { char ch='a'; printf("ch=%c\n",ch); printf("ASCII value of \'%c\'=%d\n",ch,ch); } Output: ch=a ASCII value of 'a'=97


//Character Arithmetic #include<stdio.h> main() { char ch='a'; printf("ch=%c\n",ch); ch=ch+2; printf("ASCII value of %c=%d\n",ch,ch); } Output: ch=a ASCII value of c=99 String constants (Multiple characters):

String is a sequence of characters enclosed in double quotes. The characters may be an alphabet, digit, special symbol and

white space. Each and every string ends with null character '\0'. Examples are:

"ab", "ab5", "@an", "6*7" Variable is a data name which can be used to store a data and a variable may take different values at different times during execution. Declaration and Initialization of variables: Declaration of variables: datatype v1,v2,…,vn Initialization of variables: Assign a value to a variable at the time of the variable is declared. datatype variable_name=constant;

or Assignment of an initial value to a variable is also called initialization. variable_name=constant; The process of giving initial values to variables is called initialization.


Data types: Data type specifies which type of data that we are storing in a variable. There are 3 types of data types.

1. Primary or primitive or fundamental data types 2. User defined data types 3. Derived data types 4. Empty data set

Primary data types: There four fundamental data types.

i. Integer ii. Floating point

iii. Character iv. Double precision floating point

Integer: 'C' provides three different classes of integers. They are

a) int b) short int c) long int

The difference between these 3 integers is the number of bytes to occupy the range of values.

Type Bytes Bits Range signed short int or short int

2 16 -32768 to 32767

signed int or int 2/4 16/32 -32768 to 32767 or -2147483648 to 2147483647

signed long int or long int

4 32 -2147483648 to 2147483647

unsigned short int 2 16 0 to 65535 unsigned int 2/4 16/32 0 to 65535 or 0 to 4294967295 unsigned long int 4 32 0 to 4294967295 Integers are whole numbers with a range of values supported by a particular machine. Integers occupy one word of storage, and since the word sizes of machines vary (typically 16 or 32 bits).


The size of an integer that can be stored depends on the computer. Signed integer uses one bit for sign and 15 bits for the magnitude of the number. Formula to find number of bits occupied by data type when number of bytes is known:

-2n-1 to 2n-1 - 1 Floating point types: Floating point or real numbers are stored in 32 bits (on all 16 bit and 32 bit machines) with 6 bits precision. 3 classes of floating point types:

i. float ii. double

iii. long double

Type Bytes Bits Range Precision float 4 32 3.4E-38 to 3.4E+38 6 bits double 8 64 1.7E-308 to 1.7E+308 14 bits long double 12 96 3.4E-4932 to 1.1E+4932 19 bits Character types: A single character can be defined as a character type data.

Type Bytes Bits Range signed char 1 8 -128 to 127 unsigned char 1 8 0 to 255

//Program to find number of bytes occupied by primary data types: #include<stdio.h> main() { printf("signed char size=%d\n",sizeof(char)); printf("signed short int size=%d\n",sizeof(short int)); printf("signed int size=%d\n",sizeof(int)); printf("signed long int size=%d\n",sizeof(long int)); printf("unsigned char size=%d\n",sizeof(unsigned char)); printf("unsigned int size=%d\n",sizeof(unsigned int));


printf("unsigned short int size=%d\n",sizeof(unsigned short int)); printf("unsigned long int size=%d\n",sizeof(unsigned long int)); printf("float size=%d\n",sizeof(float)); printf("double size=%d\n",sizeof(double)); printf("long double size=%d\n",sizeof(long double)); } Output: signed char size=1 signed short int size=2 signed int size=4 signed long int size=4 unsigned char size=1 unsigned int size=4 unsigned short int size=2 unsigned long int size=4 float size=4 double size=8 long double size=12

User defined data types:

'C' supports a feature known as “type definition” that allows users to define an identifier that would represent an existing data type.

The user defined data type identifier can later be used to declare variables. General form: where type is any existing data type, identifier is a new name given to the data type. Examples: typedef int units; typedef float marks; units u1,u2; marks m1, m2;

typedef type identifier


The main advantage of typedef is that we can create meaningful data type names for increasing the readability of the program.

typedef is mainly used in the concepts of structure and union. Example program: #include<stdio.h> int main() { typedef int units; typedef float marks; units a,b; marks x,y; printf("Enter 2 values\n"); scanf("%d%d",&a,&b); printf("Enter 2 values\n"); scanf("%f%f",&x,&y); printf("a=%d\tb=%d\n",a,b); printf("x=%f\ty=%f\n",x,y); } Output: Enter 2 values 5 6 Enter 2 values 1.9 6.7 a=5 b=6 x=1.900000 y=6.700000

Enumerated data type provided by ANSI standard. It is defined as: enum identifier {value1,value2,…,valuen};

Where identifier is a user defined enumerated data type, which can be used to declare variables which can have one of the values enclosed within the braces (known as enumeration constants).

After this definition, we can declare variables to be of this 'new' type. enum identifier v1,v2,…,vn can only have one of the values value1, value2, …, valuen.


The assignments are: v1=value3; v5=value1; Example: enum day {Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday}; enum day weekst, weekend; weekst=Monday; weekend=Thursday; Example program: #include<stdio.h> main() { enum day {Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday}; enum day weekst,weekend; weekst=Monday; weekend=Thursday; printf("weekst=%d\nweekend=%d\n",weekst,weekend); } Output: weekst=0 weekend=3

The compiler automatically assigns integer digits from 0 to all enumerated constants.

0 for value1, 1 for value2, 2 for value3, 3 for value4, 4 for value5, 5 for value6, 6 for value7

Automatic assignments can be overridden by using the following: enum day {Monday, Tuesday=5, Wednesday, Thursday, Friday, Saturday, Sunday};


Example program: #include<stdio.h> main() { enum day {Monday, Tuesday=5, Wednesday, Thursday, Friday, Saturday, Sunday}; enum day weekst,weekend; weekst=Tuesday; weekend=Thursday; printf("weekst=%d\nweekend=%d\n",weekst,weekend); } Output: weekst=5 weekend=7

The definition and declaration can be combined in one statement as follows:

enum day {Monday, Tuesday, Wednesday, Thursday, Friday, Saturday} weekst, weekend; #include<stdio.h> main() { enum day { Monday, Tuesday=5, Wednesday,Thursday, Friday, Saturday} weekst,weekend; weekst=Tuesday; weekend=Thursday; printf("weekst=%d\nweekend=%d\n",weekst,weekend); } Type qualifiers: We can change the properties of primitive or fundamental data type. There are two type qualifiers:

i. const for constant ii. volatile


const: const is a new data type qualifier defined by ANSI standard. Example: const int classsize=60; This tells the compiler that the value of the int variable classsize must not be modified by the program. Example program:

1. #include<stdio.h> 2. main() 3. { 4. const int classsize=60; 5. printf("classsize=%d\n",classsize); 6. classsize=classsize*3; 7. printf("classsize=%d\n",classsize); 8. }

Note: The compiler gives an error at line number 6: assignment of read-only variable 'a'. volatile: ANSI standard defines qualifier volatile that could be used tell explicitly the compiler that a variable’s value may be changed at any time by some external sources (from outside the program). Example: volatile int a; Example program: #include<stdio.h> main() { volatile int a=5; printf("a=%d\n",a); a=a*4; printf("a=%d\n",a); } Output: a=5 a=20

Unit-I Chapter 2 C Tokens: Character set, Identifiers ...

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