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    LAB 5 Compiler Construction

    Uploaded by

    Naveed Akbar Mughal
    Here is a regular expression to find all words starting with 't' or 'm' in the given document: ^(t|m)\w+$ This regular expression will: ^ - Assert position at start of the string (t|m) - Match a single character present in the list below t - 't' m - 'm' \w+ - Match any word character (equal to [a-zA-Z0-9_]) + Quantifier — Matches between one and unlimited times $ - Assert position at end of the string So this regular expression will match words starting with either 't' or 'm' followed by one or more word characters.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd

    LAB 5 Compiler Construction

    Uploaded by

    Naveed Akbar Mughal
    47 views4 pages
    Here is a regular expression to find all words starting with 't' or 'm' in the given document: ^(t|m)\w+$ This regular expression will: ^ - Assert position at start of the string (t|m) - Match a single character present in the list below t - 't' m - 'm' \w+ - Match any word character (equal to [a-zA-Z0-9_]) + Quantifier — Matches between one and unlimited times $ - Assert position at end of the string So this regular expression will match words starting with either 't' or 'm' followed by one or more word characters.

    Original Description:

    Compiler Construction LAB 5

    Copyright

    © © All Rights Reserved

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    Here is a regular expression to find all words starting with 't' or 'm' in the given document: ^(t|m)\w+$ This regular expression will: ^ - Assert position at start of the string (t|m) - Match a single character present in the list below t - 't' m - 'm' \w+ - Match any word character (equal to [a-zA-Z0-9_]) + Quantifier — Matches between one and unlimited times $ - Assert position at end of the string So this regular expression will match words starting with either 't' or 'm' followed by one or more word characters.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    47 views4 pages

    LAB 5 Compiler Construction

    Uploaded by

    Naveed Akbar Mughal
    Here is a regular expression to find all words starting with 't' or 'm' in the given document: ^(t|m)\w+$ This regular expression will: ^ - Assert position at start of the string (t|m) - Match a single character present in the list below t - 't' m - 'm' \w+ - Match any word character (equal to [a-zA-Z0-9_]) + Quantifier — Matches between one and unlimited times $ - Assert position at end of the string So this regular expression will match words starting with either 't' or 'm' followed by one or more word characters.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    of 4

    Spring 2021 Session 2018-22

    LAB # 05
    Statement Purpose:
    Lexical analysis is the first phase of a compiler. It takes the modified source code from language
    preprocessors that are written in the form of sentences. The lexical analyzer breaks these
    syntaxes into a series of tokens, by removing any whitespace or comments in the source code. If
    the lexical analyzer finds a token invalid, it generates an error. The lexical analyzer works
    closely with the syntax analyzer. It reads character streams from the source code, checks for
    legal tokens, and passes the data to the syntax analyzer when it demands.

    In programming language, keywords, constants, identifiers, strings, numbers, operators and


    punctuations symbols can be considered as tokens.

    Activity Outcomes:
    This lab teaches you
     How to recognize keywords from a source program written in a high level language

    Instructor Note:

    Students should know how to write regular expressions in C#


    Introduction

    A regular expression is a pattern that describes a set of strings. Regular expressions are
    constructed analogously to arithmetic expressions by using various operators to combine smaller
    expressions.
    The fundamental building blocks are the regular expressions that match a single character. Most
    characters, including all letters and digits, are regular expressions that match themselves. Any
    meta character with special meaning may be quoted by preceding it with a backslash. In basic
    regular expressions the metacharacters "?", "+", "{", "|", "(", and ")" lose their special meaning;
    instead use the backslashed versions "\?", "\+", "\{", "\|", "\(", and "\)".

    Regular Expression for keywords

    [int | float | double | char]


    Lab Activities:
    Activity 1:
    Design a regular expression for keywords

    Solution:
    This example replaces extra white space:

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using System.Windows.Forms;
    using System.Text.RegularExpressions;
    namespace Sessional1
    {
    public partial class Form1 : Form
    {
    public Form1()
    {
    InitializeComponent();

    }
    private void button1_Click(object sender, EventArgs e)
    {
    // take input from a richtextbox/textbox
    String var = richTextBox1.Text;
    // split the input on the basis of space
    String[] words = var.Split(' ');
    // Regular Expression for variables
    Regex regex1 = new Regex(@"^[int | float | char] $");
    for (int i = 0; i < words.Length; i++)
    {
    Match match1 = regex1.Match(words[i]);
    if (match1.Success)
    {
    richTextBox2.Text += words[i] + " ";
    }
    else {
    MessageBox.Show("invalid "+words[i]);
    }
    }
    }
    }
    Home Activities:

    Activity 1:
    Design a regular expression for finding all the words starting with ‘t’ and ‘m’ in the following
    document.

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