The lab is designed to introduce the students to the basics steps of a compiler Design. After that the lab will focus and dive deep into the first compilation step which is Lexical analysis. Basic
techniques of coding and required tools will also be shown to students.
II. Lesson Fit:
The lab gives a hand on experience of the knowledge of theory class.
III. Learning Outcome:
After this lecture, the students will be able to:
a. Understand and visualize the Lexical Analysis step.
b. Identifying the “Token” for a particular program.
c. Creating a version of Lexical analyzer.
IV. Anticipated Challenges and Possible Solutions
a. Finding out the identifiers and numerical values from the given code. Possible
Solutions:
i. Use regular expressions.
ii. Use methods of java String class.
V. Acceptance and Evaluation
If a task is a continuing task and one couldn’t finish within time limit, he/she will continue from there in the next Lab, or be given as homework. He/ she has to submit the code and have to face a short viva. A
deduction of 30% marks is applicable for late submission. The marks distribution is as follows:
Code: 0%
Viva: 100%
VI. Activity Detail
a.Hour: 2
Discussion: Basic Concepts & Regular Expressions
1. What does a Lexical Analyzer do?
2. How does it Work?
3. Formalizing Token Definition & Recognition
Problem task:
i. Task 1 (Page 3- 4)
In this assignment, your job is to program a simple lexical analyzer that will build a symbol table from given stream of chars. You will need to read a file named "input.txt" to collect all chars. For simplicity, input file will be a C program without headers and methods. Then you will identify all the numerical values,
identifiers, keywords, math operators, logical operators and others
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[distinct]. See the example for more details. You can assume that there will be a space after each keyword.
But, removal of space will add bonus points.
Lab 1: Activity List
Task 1: For the following sample program find all the tokens.
Note that a lexical Analyzer is responsible for
1. Scan Input
2. Remove WS, NL, ...
3. Identify Tokens
4. Create Symbol Table (ST)
5. Insert Tokens into ST
6. Generate Errors
7. Send Tokens to Parser
Fig 1: Lexical Analyzer
Input:
int a, b, c; float d, e; a = b = 5; c = 6; if ( a > b) {
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e = d - 2.0;
}
else {
d = e + 6.0; b = a + c;
}
Output:
Keywords: int, float, if, else
Identifiers: a, b, c, d, e
Math Operators: +, -, =
Logical Operators: >
Numerical Values: 5, 6, 2.0, 6.0
Others: , ; ( ) { }
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