Difference between revisions of "PLC Laboratory 2"

From Marek Běhálek Wiki
Jump to navigation Jump to search
Line 1: Line 1:
−
== Interpreter of Arithmetic Expressions ==
+
== Lexical analyzer ==
  
−
Implement an interpreter of arithmetic expressions. These expressions contain <code>+, -, *, /</code> operators (with common priorities and left associativity) and parentheses.  
+
Write a program, that reads an input and converts it into a sequence of lexical symbols – tokens. Each token composes from a type and possibly a value.  
  
−
To simplify the task, consider we have only binary operators. There are no unary operators in our language. Moreover, we can use only positive integers in our expressions.
+
The tokens definition depends on you, and it is considered a part of the solution.
  
 
== Input specification ==
 
== Input specification ==
  
−
The first line of the input contains a number <code>N</code>. It defines the number of expressions your program should evaluate. These expressions are on next <code>N</code> lines. Each line contains exactly one expression.  
+
The input may be containing the following symbols:
 +
* ''identifiers'' - consisting of a sequence of letters and numbers starting with a letter
 +
* numbers - formed by a sequence of decimal digits
 +
* operators - symbols '+', '-', '*' and '/',
 +
* delimiters - symbols '(', ')' and ';',
 +
* keywords - <code>div</code> and <code>mod</code>.
 +
 
 +
Symbols can be separated by a sequence of spaces, tabs, and line breaks.  
 +
 
 +
Notes are preceded by a sequence <code>//</code> and continue to the end of the line.
 +
  
 
== Output specification ==
 
== Output specification ==

Revision as of 08:33, 26 January 2022

Lexical analyzer

Write a program, that reads an input and converts it into a sequence of lexical symbols – tokens. Each token composes from a type and possibly a value.

The tokens definition depends on you, and it is considered a part of the solution.

Input specification

The input may be containing the following symbols:

  • identifiers - consisting of a sequence of letters and numbers starting with a letter
  • numbers - formed by a sequence of decimal digits
  • operators - symbols '+', '-', '*' and '/',
  • delimiters - symbols '(', ')' and ';',
  • keywords - div and mod.

Symbols can be separated by a sequence of spaces, tabs, and line breaks.

Notes are preceded by a sequence // and continue to the end of the line.


Output specification

For each expression write one line containing the result – the computed value of the expression. If there is any error in the input, write text ERROR instead.

Example

  • Input
2
2 * (3+5)
15 - 2**7
  • Output
16
ERROR
Retrieved from "http://behalek.cs.vsb.cz/wiki/index.php?title=PLC_Laboratory_2&oldid=2963"