04 Lex Something

%{
#include <stdio.h>
#include <stdlib.h>
%}
%%
[01]+ {
    int num = 0, base = 2, exp;
    int result;
    int len = strlen(yytext);
    for (int i = 0; i < len; i++) {
        if (yytext[i] == '1') {
        result = 1;
        exp = len-i-1;
            while (exp != 0) {
            result *= base;
            --exp;
        }
        num += result;
        }
    }
    if (num == 0) {
        printf("The input is not a power of two\n");
    } else if ((num & (num-1)) == 0) {
        printf("The input is a power of two\n");
    } else {
        printf("The input is not a power of two\n");
    }
}
. {
    printf("Invalid input\n");
}
%%
int main() {
    yylex();
    return 0;
}

%{
#include <stdio.h>
int line_number = 1;
%}

%%

\n {
    line_number++;
    printf("\n%d: ", line_number);
}

. {
    printf("%c", yytext[0]);
}

%%

int main() {
    FILE *input_file = fopen("input.c", "r");
    if (input_file == NULL) {
        printf("Error: cannot open file.\n");
        return 1;
    }
    yyin = input_file;
    printf("1: ");
    yylex();
    fclose(input_file);
    return 0;
}

%{
#include <stdio.h>
#include <stdbool.h>
bool in_block_comment = false;  /* initialize in_block_comment flag to false */
bool in_line_comment = false;   /* initialize in_line_comment flag to false */
%}

%%

"/*"    { in_block_comment = true; }  /* set in_block_comment flag to true on start of block comment */
"*/"    { in_block_comment = false; }  /* set in_block_comment flag to false on end of block comment */
"//"    { in_line_comment = true; }   /* set in_line_comment flag to true on start of line comment */
\n      {
            if (in_line_comment) { in_line_comment = false; }  /* set in_line_comment flag to false on end of line */
            if (!in_block_comment) { fputc('\n', yyout); }     /* write newline character to output file if not in comment */
         }
.       { if (!in_block_comment && !in_line_comment) { fputc(yytext[0], yyout); } }  /* write character to output file if not in comment */
%%

int main(int argc, char** argv) {
    if (argc != 3) {
        printf("Usage: %s input_file output_file\n", argv[0]);
        return 1;
    }

    FILE* input_file = fopen(argv[1], "r");
    if (input_file == NULL) {
        printf("Error: could not open input file %s\n", argv[1]);
        return 1;
    }

    FILE* output_file = fopen(argv[2], "w");
    if (output_file == NULL) {
        printf("Error: could not open output file %s\n", argv[2]);
        return 1;
    }

    yyin = input_file;
    yyout = output_file;
    yylex();

    fclose(input_file);
    fclose(output_file);
    return 0;
}

%{
#include <stdio.h>
%}

%%

^[0-9]{4}[A-Za-z0-9]{2}(PS|TS)[0-9]{4}[HPUG]$  {
    printf("Year of Joining: %c%c%c%c\n",yytext[0], yytext[1],yytext[2], yytext[3]);
    printf("Specialization: %c%c\n", yytext[4], yytext[5]);
    printf("Thesis/Practice School: %c%c\n", yytext[6], yytext[7]);
    printf("Registration Index: %c%c%c%c\n", yytext[8], yytext[9], yytext[10], yytext[11]);
    printf("Campus: %c\n", yytext[12]);
}
.  {
    printf("Invalid roll number format.\n");
}

%%

int main() {
    yylex();
    return 0;
}