Lex program ~ Read and copy file content

This lex program will read an input file and copy the content with line number to another file. %{ #include<stdio.h> #include<string.h> char line[20]; int count=0,i=0; FILE *out; %} %% ['\n'] { fprintf(out,"%d %s\n",++count,line);} (.*) { strcpy(line,yytext); }%% main() { yyin=fopen("in.c","r"); out=fopen("out.c","w"); yylex(); getch(); } int yywrap() { return 1; } input main() { int i=9, j=900,k=115; printf("%d,i+j+k); } output file 1 main() 2 { 3 int i=9, j=900,k=115; 4 printf("%d,i+j+k); 5 } 6...

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Lex- Collect Tokens and sort

Hello friend,   Here I am with an interesting Lex program which sorts all the nubers from input file and sort them. If you are well-familiarised with lex paradigm, it is very easy task. Things to remember: The definition [0-9]+ can detect all the numbers from input The number detected at present will be pointed by yytext and have length yyleng Whenever a new token (here a number) is detected, yytext will be replaced with new value.  Logic Read the input If a number is detected, store it in an array (we can use yytext and yyleng for this). Read each digit --> multiply with 10 --> add next digit -->continue upto last digit.   for eg, to read 123 initialise num=0; read 1--> num=num*10+1-->num=0+1-->num=1 read 2--> num=num*10+2-->num=10+2-->num=12 read...

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Lex and Yacc in Windows 7 - Compile and Run

Hi Friend, I was in search for a long time to get a platform in windows-7 to run lex and Yacc ,for academic purposes. Many of my friends also had the same problem and often forced to choose Linux only for merely executing Lex & Yacc programs..!!! At last, I found one solution and its my pleasure to share it with all of you.!!  :) Its very simple.You need to download two very small files. You have to download two executable( i.e.,   .exe files). In total,its size may have about 370KB. To download them click the links below. Link 1:   Flex Link 2:  Bison Save both files in same place....

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LEX program to check a Date (dd/mm/yyyy)

Hello dude..                I would like to discuss a problem asked by my teacher in our internal lab exam- LEX program to check the validity of a Date. Ahem..In normal programming (i.e, that with C or Java) this is not a big deal!! But in Lex paradigm,it require some more effort..!!                                                 ...

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C Program to generate Intermediate code

#include<stdio.h> #include<ctype.h> #include<string.h> main() { char a[20]; int i=2,n; printf("Exp  :"); scanf("%s", a); if(isdigit(a[0])) printf("MVI A,%c\n",a[0]); else printf("MOV A,%c\n",a[0]); n=strlen(a); while(i<n) { switch(a[i]) { case '+':printf("ADD B\n");i+=3;break; case '-':printf("SUB B\n");i+=3;break; default:if(isdigit(a[i])) printf("MVI B,%c\n",a[i]); else printf("MOV B,%c\n",a[i]); i--; } }...

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LEX program to check the syntax of SCANF statement

%{ #include<stdio.h> #include<ctype.h> int i=0,j=0; %}a "%d"|"%f"|"%c"|"%s" id [a-zA-Z][a-zA-Z0-9]* %% scanf\((\"({a}*|.*)*\"(,\&{id})*\))\; {for(i=0;i<yyleng;i++) {if(yytext[i]=='%') j++; if(yytext[i]==',') j--; } if(j==0) printf("Correct"); else printf("Incorrect"); } %% main() { yyin=fopen("sample.c","r"); yylex(); } int yywrap() { return 1; }        ...

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LEX program to check the syntax of PRINTF statement

%{ #include<stdio.h> #include<ctype.h> int i=0,j=0; %}a "%d"|"%f"|"%c"|"%s" id [a-zA-Z][a-zA-Z0-9]* %% printf\((\"({a}*|.*)*\"(,{id})*\))\; {for(i=0;i<yyleng;i++) { if(yytext[i]=='%') j++; if(yytext[i]==',') j--; } if(j==0) printf("Correct..!!"); else printf("Incorrect..!!"); } %% main() { yyin=fopen("sample.c","r"); yylex(); } int yywrap() { return 1; }       Explanation: Well, checking syntax of printf statement is very easy. The syntax should be "printf" followed by "(" and  " . It can include a usual string or %d,%f type expression delimited by another ". The entities specified...

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Lex program to check the syntax of FOR loop

%{ #include<stdio.h> #include<ctype.h> int c=1; %} op "++"|"--" rop "<"|">"|"<="|">="|"=="|"!=" id [a-zA-Z][a-zA-Z0-9]* no [0-9]* pp [\n] %% for\(({id}=({no}|{id}))?\;{id}{rop}({id}|{no})\;{id}{op}\){pp}+\{(.*\n)*.*\} {printf("correct");c=0;} %% main() { yyin=fopen("file11.c","r"); yylex(); if(c==1) printf("incorrect"); } int yywrap() { return 1;...

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LEX Program to identify Keywords and convert it into uppercase

Guys, apply simple logic. Detect all keywords( This program deal with a small number of keywods for sake of simplicity). On detecting any keyword in C, convert it into uppercasr letter using the funtion 'toupper' . Game over!! %{#include<stdio.h> int i; %}keyword main|int|scanf|printf|if|else %% {keyword} {  for(i=0;i<yyleng;i++)  printf("%c",toupper(yytext[i]));    } %% main() { yyin=fopen("num.c","r"); yylex(); } int yywrap() { return 1; } OutputLet num.c contains following program fragment. main() { int num; scanf("%d",&num); if(num%2)printf("Odd"); else printf("Even") } The output will be, MAIN() { INT num; SCANF("%d",&num); IF(num%2)PRINTF("Odd"); ELSE...

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LEX Program to eliminate all whitespaces

Hi Guys, This lex program is aimed to eliminate all whitespaces from an input file. As u think, this is not at all a difficult job. We have to simply detect single blank ' ' or tab '\t' or a newline '\n' and delete them in output. That's all..!!!! %{ #include<stdio.h> %} %% [\n\t ' '] {}; %% main() { yyin=fopen("myfile.txt","r"); yylex(); } int yywrap() { return 1; } ____________________________________________________________________ Look @ the example: Basic datatypes in C are: int   char  float   double output will be BasicdatatypesinCare:intcharfloatdouble ...

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LEX Program to delete all comments

No Comments  :) This lex program is intended to eliminate comments from a C program. This task is simple since in a C program, comments will be associated only with '//' or '/*...*/ only. So our aim is to detect the occurence of these characters and ignore subsequent comments. %{ #include<stdio.h> %} %% \/\/.* ; \/\*(.*\n)*.*\*\/ ; %% main() { yyin=fopen("mypgm.c","r"); yylex(); } int yywrap() { return 1; } \/\/.* ; eliminates single line coments. i.e., comments of the form ' //comment.. .. .. ;' It simply look on '/'immediately followed by another '/' and ignore that line. \/\*(.*\n)*.*\*\/ ; eliminates multiple...

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LEX Program to count the number of lines, words and letters

Howdy guys, Lets have a look on how a Lex programs works using a simple example. This sample programs counts the number of lines, words and characters in a text file.   Lex programming is not rocket science. You have to just apply an eight year old kid's logic. Yes, you read right. Only a school kid's logic. LOGIC Read each character from the text file : Is it a capital letter in English? [A-Z] : increment capital letter count by 1. Is it a small letter in English? [a-z] : increment small letter count by 1 Is it [0-9]? increment digit count by 1. All other characters (like '!', '@','&') are counted as special characters How...

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