LexicalAnalyzerWithFiles.c

//make a file lex.txt containing a small c prog and write the name "lex.txt" 
/* Algorithm:

 Initialize the file pointers, predefined keywords, operators in separate
arrays.
 Read every line of the input file by reading each character and
appending it to another string “line” till it encounters ‘\n’.
 Now check whether line is a comment or not.
 Run a loop through the line string and extract words from it using
special characters as delimiters.
 For each special character encountered, check whether the character
is an operator or not and then send the extracted word into the
function that will decide what category of Lexeme it is.
 If it is one of the keywords, then the output is 1, if it is a valid identifier
then output is 2, otherwise output is 0.
 Write onto the respective files according to the classified data.
 Print the number of lines as output.*/

#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>

char keywords[32][10] = {"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"};

char operators[4] = {'+', '-', '/', '*'};

FILE *inputFile, *keywordsFile, *operatorsFile, *identifiersFile, *commentsFile;

int is_alpha(int c)
{
    return (c >= 65 && c <= 90) || (c >= 97 && c <= 122);
}

int isLexeme(char word[20])
{
    int length = strlen(word), i;

    if (length < 1)
        return 0;

    for (i = 0; i < 32; i++)
        if (!strcmp(keywords[i], word))
            return 1;

    if (word[0] != '_' && !is_alpha(word[0]))
        return 0;

    return 2;
}

int isOperator(char op)
{
    int i;
    for (i = 0; i < 4; i++)
        if (op == operators[i])
            return 1;
    return 0;
}

int isSpecial(int c)
{
    if (c == '_')
        return 0;
    return (c >= 32 && c <= 47) || (c >= 58 && c <= 64) || (c >= 91 && c <= 96) || (c >= 123 && c <= 127);
}

char *trim(char *s)
{
    int i;

    while (isspace(*s))
        s++;
    for (i = strlen(s) - 1; (isspace(s[i])); i--)
        ;
    s[i + 1] = '\0';
    return s;
}

int isComment(char str[100])
{
    strcpy(str, trim(str));
    int length = strlen(str);
    if (length < 2)
        return 0;
    else if ((str[0] == str[1]) && (str[0] == '/'))
        return 1;
    else if ((str[0] == str[length - 1]) && (str[1] == str[length - 2]))
    {
        if (str[0] == '/' && str[1] == '*')
            return 1;
    }
    else
        return 0;
}

int main()
{
    printf("\nEnter the filename of a C program: ");
    char filename[20];
    gets(filename);

    inputFile = fopen(filename, "r");
    keywordsFile = fopen("Keywords.txt", "w");
    operatorsFile = fopen("Operators.txt", "w");
    commentsFile = fopen("Comments.txt", "w");
    identifiersFile = fopen("Identifiers.txt", "w");

    if (inputFile == NULL)
    {
        printf("Error while opening the file.\n");
        return 0;
    }

    int lines = 0, length, i, lex = 0;
    char c, word[20] = "", line[1000] = "", lastChar;
    while ((c = getc(inputFile)) != EOF)
    {
        if (c == '\n')
        {
            lines++;
            if (isComment(line))
            {
                fputs(line, commentsFile);
                putc('\n', commentsFile);
                strncpy(line, "", sizeof(line));
                continue;
            }
            length = strlen(line);
            for (i = 0; i < length; i++)
                if (isSpecial(line[i]))
                {
                    if (isOperator(line[i]))
                        putc(line[i], operatorsFile);

                    int lex = isLexeme(word);
                    if (lex == 1)
                    {
                        fputs(word, keywordsFile);
                        putc('\n', keywordsFile);
                    }
                    else if (lex == 2)
                    {
                        fputs(word, identifiersFile);
                        putc('\n', identifiersFile);
                    }
                    strncpy(word, "", sizeof(word));
                }
                else
                    strncat(word, line + i, 1);
            strncpy(line, "", sizeof(line));
        }
        else
            strncat(line, &c, 1);
        lastChar = c;
    }
    printf("Number of lines: %d\n", lines);
}