COP 3503 Lexical Analyzer

Problem Description

In this problem, you should implement the lexical analysis task for a limited version (i.e., the depth of the nested loops) of a programming language. Lexical analysis is the first stage that compilers parse and detect the possible syntax errors.

Ideally, any new (programming) languages can be designed and analyzed in the similar manner. You will need to analyze a Pascal-and-C-like language in this programming assignment.

Given a segment of the source code, your C++ code should analyze the code and extract all tokens, which include:

• Keywords: keywords are the words reserved by the language. They are all upper- case. In the case of this simplified language, the keywords are restricted to the set { BEGIN, END, FOR }
• Identifiers: An identifier is used to describe the variables, which are all lower-case
• Constants: Numbers like 10, ... .
• Operators: all arithmetic operations (i.e., +, -, *, and /), ++ and =
• Delimiters: like , and ;

Your C++ code should input a text file from user, which contains the expression he/she wants the compilers to analyze. Then, your code should parse the input, detect the tokens, classify them, and print out the results.

With this assignment, you will get practice with the stack implementation which is one of the most widely used data structures. Besides, you will be familiar with string processing and input parsing, which are of crucial importance in most C++ projects.

Details

1. (Data Structures:) You need to implement a stack data structure to keep track of the processing and compute the depth of the nested loops. Adding elements to the stack (push) and removing objects from it (pop) are two essential methods that must be implemented. You can use any data structure to implement the stack, e.g., arrays, linked-lists, etc.

2. (Algorithms:) Once the input expression is given, your program should decide which character should be inserted to the stack, and when the result needs to be computed. You need to detect the possible syntax errors while tracing the depth of the nested loops.

Example Run

Try to keep your output as close to the given format as possible:

In this example, the input file is "code.txt"
It contains the code segment below:
FOR (i, 10, ++)
BEGIN
FOR (j, 10, ++)
BEGAN
sum=sum + i + j;
END
END
> ./pa3.out
INPUT> Please enter the name of the input file:
code.txt
OUTPUT> The depth of nested loop(s) is 1
Keywords: FOR BEGIN END
Identifier: sum i j
Constant: 10
Operatros: ++ = +
Delimiter: ; ,
Syntax Error(s): BEGAN

Hints

1. You should get your stack data structure working well before implementing the lexical analysis task.

2. The string processing to parse the input is an essential part of this assignment. You should make sure that you parse the input correctly, and you take care of all edge cases, e.g., more than one spaces between characters, no spaces, etc.