System Software Lab 6 | Read Now
System Software VTU Lab
Program 6
a) Write a LEX program to eliminate comment lines in a C program and copy the resulting program into a separate file.
b) Write the YACC program to recognize valid identifiers, operators, and keywords in the given text (C program) file.
Steps in writing LEX Program:
- Step – Using gedit create a file with extension .l For example: prg1.l
- Step – lex prg1.l
- Step – cc lex.yy.c –ll
- Step – ./a.out
Steps in writing YACC Program:
- Step: Using gedit editor create a file with extension y. For example: gedit prg1.y
- Step: YACC –d prg1.y
- Step: lex prg1.l
- Step: cc y.tab.c lex.yy.c -ll
- Step: /a.out
System Software Lab 6a Code [lab6.l]
%{ #include<stdio.h> int sl=0; int ml=0; %} %% "/*"[a-zA-Z0-9' '\t\n]+"*/" ml++; "//".* sl++; %% main() { yyin=fopen("f1.c","r"); yyout=fopen("f2.c","w"); yylex(); fclose(yyin); fclose(yyout); printf("\n Number of single line comments are = %d\n",sl); printf("\nNumber of multiline comments are =%d\n",ml); }
f1.c
#include<stido.h> int main() { // this is a comment printf("hello"); /* this is another comment */ }
System Software lab 6 – Output
![System Software](https://www.vtuloop.com/wp-content/uploads/2021/10/SS-OUTPUT6a.jpg)
System Software Lab6.b Code
lab6.l
%{ #include <stdio.h> #include "y.tab.h" extern yylval; %} %% [ \t]; [+|-|*|/|=|<|>] {printf("operator is %s\n",yytext);return OP;} [0-9]+ {yylval = atoi(yytext); printf("numbers is %d\n",yylval); return DIGIT;} int|char|bool|float|void|for|do|while|if|else|return|void {printf("keyword is %s\n",yytext);return KEY;} [a-zA-Z0-9]+ {printf("identifier is %s\n",yytext);return ID;} . ; %%
lab6.y
%{ #include <stdio.h> #include <stdlib.h> int id=0, dig=0, key=0, op=0; %} %token DIGIT ID KEY OP %% input: DIGIT input { dig++; } | ID input { id++; } | KEY input { key++; } | OP input {op++;} | DIGIT { dig++; } | ID { id++; } | KEY { key++; } | OP { op++;} ; %% #include <stdio.h> extern int yylex(); extern int yyparse(); extern FILE *yyin; main() { FILE *myfile = fopen("inputfile.c", "r"); if (!myfile) { printf("I can't open inputfile.c!"); return -1; } yyin = myfile; do{ yyparse(); }while (!feof(yyin)); printf("numbers = %d\nKeywords = %d\nIdentifiers = %d\noperators = %d\n",dig, key,id, op); } void yyerror() { printf("EEK, parse error! Message: "); exit(-1); }
inputfile.txt
#include<stdio.h> int main() { int a ; int b ; a = 1 ; b = 2 ; a = a+b; return 0 ; }
System Software lab6b – Output
![](https://www.vtuloop.com/wp-content/uploads/2021/10/SS-OUTPUT6b.jpg)