1 to 3 lex

1. Write a C program to solve an arithmetic expression using +, - , * , and / operators.

#include <stdio.h>

int main() {
   float num1, num2, result;
   char op;

   printf("Enter an arithmetic expression using +, -, *, and / operators: ");
   scanf("%f %c %f", &num1, &op, &num2);

   switch(op) {
      case '+':
         result = num1 + num2;
         break;
      case '-':
         result = num1 - num2;
         break;
      case '*':
         result = num1 * num2;
         break;
      case '/':
         result = num1 / num2;
         break;
      default:
         printf("Invalid operator.");
         return 1;
   }

   printf("%.2f %c %.2f = %.2f", num1, op, num2, result);
   return 0;
}

2a. Write a program in C to convert a declaration statement into a sequence of tokens
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_TOKENS 100

int main() {
    char declaration[100];
    char tokens[MAX_TOKENS][20];
    int num_tokens = 0;
    char* token;
    
    printf("Enter a declaration statement:\n");
    fgets(declaration, 100, stdin);
    
    token = strtok(declaration, " ");
    while (token != NULL && num_tokens < MAX_TOKENS) {
        strcpy(tokens[num_tokens], token);
        num_tokens++;
        token = strtok(NULL, " ");
    }
    
    printf("The sequence of tokens is:\n");
    for (int i = 0; i < num_tokens; i++) {
        printf("%s\n", tokens[i]);
    }
    
    return 0;
}

2b. Write a program in C to convert control flow statements (condition and loops into a sequence of tokens)

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

#define MAX_TOKENS 100

int main() {
    char statement[100];
    char tokens[MAX_TOKENS][20];
    int num_tokens = 0;
    char* token;
    
    printf("Enter a control flow statement:\n");
    fgets(statement, 100, stdin);
    
    token = strtok(statement, " ();{\n\t");
    while (token != NULL && num_tokens < MAX_TOKENS) {
        strcpy(tokens[num_tokens], token);
        num_tokens++;
        token = strtok(NULL, " ();{\n\t");
    }
    
    printf("The sequence of tokens is:\n");
    for (int i = 0; i < num_tokens; i++) {
        printf("%s\n", tokens[i]);
    }
    
    return 0;
}

2c. Write a program in C to convert I/O statements (printf and scanf) into a sequence of tokens

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

#define MAX_TOKENS 100

int main() {
    char statement[100];
    char tokens[MAX_TOKENS][20];
    int num_tokens = 0;
    char* token;
    
    printf("Enter an I/O statement (printf or scanf):\n");
    fgets(statement, 100, stdin);
    
    token = strtok(statement, " ();{\n\t\"");
    while (token != NULL && num_tokens < MAX_TOKENS) {
        strcpy(tokens[num_tokens], token);
        num_tokens++;
        token = strtok(NULL, " ();{\n\t\"");
    }
    
    printf("The sequence of tokens is:\n");
    for (int i = 0; i < num_tokens; i++) {
        printf("%s\n", tokens[i]);
    }
    
    return 0;
}

3a. Write a program in Lex to count the number of words in a string.
%{
int word_count = 0;
%}

%%
[a-zA-Z]+   { word_count++; }  /* Match one or more letters */
[ \t\n]+    { /* Ignore whitespace */ }
.           { /* Ignore everything else */ }
%%

int main() {
    yylex(); /* Run the lexer */
    printf("Number of words: %d\n", word_count);
    return 0;
}
lex wordcount.l
cc lex.yy.c -o wordcount -ll
./wordcount

3b. Write a program in Lex to count the number of vowels and consonants in a string
%{
int vowel_count = 0;
int consonant_count = 0;
%}

%%
[aAeEiIoOuU]   { vowel_count++; }     /* Match vowels */
[a-zA-Z]       { consonant_count++; } /* Match consonants */
[ \t\n]+       { /* Ignore whitespace */ }
.              { /* Ignore everything else */ }
%%

int yywrap() {
    return 1;
}

int main() {
    char input[256];
    printf("Enter a string: ");
    fgets(input, sizeof(input), stdin); /* Read input from user */
    yy_scan_string(input); /* Set the input for the lexer */
    yylex(); /* Run the lexer */
    printf("Number of vowels: %d\n", vowel_count);
    printf("Number of consonants: %d\n", consonant_count);
    return 0;
}

flex lex.l
gcc lex.yy.c
a.exe