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1. 20DCE096 CE442: DESIGN OF LANGUAGE PROCESSOR 5
PRACTICAL - 2
Aim: Implement a lexical analyser using C.
Code:
#include <stdio.h>
#include <string.h>
#include <ctype.h>
// Define token types
enum TokenType {
KEYWORD,
IDENTIFIER,
LITERAL,
OPERATOR,
PUNCTUATION,
PREPROCESSOR_DIRECTIVE
};
// Function to classify and print tokens
void printToken(char* lexeme, enum TokenType type) {
char* tokenTypeStr;
switch (type) {
case KEYWORD:
tokenTypeStr = "Keyword";
break;
case IDENTIFIER:
tokenTypeStr = "Identifier";
break;
case LITERAL:
tokenTypeStr = "Literal";
break;
case OPERATOR:
tokenTypeStr = "Operator";
break;
case PUNCTUATION:
tokenTypeStr = "Punctuation";
break;
case PREPROCESSOR_DIRECTIVE:
tokenTypeStr = "Preprocessor Directive";
break;
default:
tokenTypeStr = "Unknown";
}
printf("Type: %s, Lexeme: %sn", tokenTypeStr, lexeme);

2. 20DCE096 CE442: DESIGN OF LANGUAGE PROCESSOR 6
}
int main() {
FILE *file = fopen("input.txt", "r"); // Open the file in read mode
if (file == NULL) {
perror("Error opening file");
return 1;
}
char input[1000];
char lexeme[1000];
int i = 0;
int j = 0;
while (fgets(input, sizeof(input), file) != NULL) {
for (i = 0; i < strlen(input); i++) {
// Check for keywords
if (isalpha(input[i])) {
j = 0;
while (isalpha(input[i]) || isdigit(input[i])) {
lexeme[j++] = input[i++];
}
lexeme[j] = '0';
// You would have a list of keywords to compare against
if (strcmp(lexeme, "if") == 0 || strcmp(lexeme, "while") == 0 || strcmp(lexeme, "for") == 0)
{
printToken(lexeme, KEYWORD);
} else {
printToken(lexeme, IDENTIFIER);
}
i--;
}
// Check for numeric literals
else if (isdigit(input[i])) {
j = 0;
while (isdigit(input[i]) || input[i] == '.') {
lexeme[j++] = input[i++];
}
lexeme[j] = '0';
printToken(lexeme, LITERAL);
i--;
}

3. 20DCE096 CE442: DESIGN OF LANGUAGE PROCESSOR 7
// Check for operators and punctuation
else if (strchr("+-*/=<>,;(){}", input[i]) != NULL) {
lexeme[0] = input[i];
lexeme[1] = '0';
printToken(lexeme, OPERATOR);
}
// Check for preprocessor directives
else if (input[i] == '#') {
j = 0;
while (input[i] != '0' && input[i] != 'n') {
lexeme[j++] = input[i++];
}
lexeme[j] = '0';
printToken(lexeme, PREPROCESSOR_DIRECTIVE);
}
}
}
fclose(file); // Close the file
return 0;
}
Output:
Conclusion: In this practical we implement lexical analyzer, which read content of text file and
analyze it.
Grade:
Signature:
Remarks: