Description

UCS1602 – Compiler Design
Programming Assignment-1 – Implementation of lexical analyser and
symbol table

The Goal
In the first programming assignment, you will get your compiler off to a great start by implementing Lexical analyzer or Scanner using C. Your scanner will run through the source program recognizing C tokens in the order in which they are read, until end of file is reached. When an identifier is encountered, it should be stored in symbol table with its attributes. Symbol table consist of the attributes identifier name, type, no of bytes, location and value. Your scanner should identify the tokens categorized below and print it.

C Programming Language: Lexical construct
Here is the summary of the token types in C programming language

The following are keywords. They are all reserved:
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

An identifier is a sequence of letters, digits and underscores, starting with a letter. C language is case sensitive. Eg; “if” is a keyword, but “IF” is an identifier. Binky and binky are two different identifiers.

C language adopts two types of comments. A single-line comment is started by // and extends to the end of the line. Multi-line comments start with /* and end with the first subsequent */. Multi-line comments do not nest. If a file ends with an unterminated comment, the scanner should report an error.

An integer constant can either be specified in decimal (base 10) or hexadecimal (base 16). A decimal integer is a sequence of decimal digits (0-9). A double constant is a sequence of digits, a period, followed by any sequence of digits. A string constant is a sequence of characters enclosed in double quotes. Strings can contain any character except a new line or double quote. A string must start and end on a single line; it cannot be split over multiple lines:

Arithmetic operators
+, -, *, /, %
Arithmetic assignment operators
+=, -=, *=, /=, %=
Logical operators &&, ||, !
Relational operators
<. <=, >, >=, ==, !=
Bitwise operators
^, &, |, <<, >>
Unary operators
-, ++, – –
Assignment operator
=
Special character
; , . [ ] ( ) { } []

The following are identified as function calls printf(), scanf(), getch(), clrscr(),

Develop a scanner that will recognize all the above specified tokens. Test your program for all specified tokens. Example input and output specification is given below.

Example input source program #include<stdio.h> main() { int a=10,b=20; if(a>b) printf(“a is greater”); else printf(“b is greater”);
}

Output:
#include<stdio.h> – preprocessor directive
main() – function call { – special character int – keyword a – identifier
= – assignment operator
10 – integer constant , -special character b – identifier
= – assignment operator
20 – integer constant ; – special character if – keyword ( – special character a – identifier > – relational operator b – identifier
) – special character printf(“a is greater”) – function call ; – special character printf(“b is greater”) – function call
; – special character
} – special character

Content of Symbol Table

Identifier
Name Type No of bytes Address Value
a int 2 1000 10
b int 2 1002 20