Question

Note: The question needs to be answered in "C Programming Languange ". And after the question find 3 pages for needed informations.

Spring CE4717 Language Processors Q1. Consider the following LEx program. return R1 return R2 return R3 return R4 return R5; return R6; IA-2a-z)[A-Za-z0-9]- -2 10-91+ 10-9a-EA-FI Ihi] [01] [01] 이삐 t Vtin) int main (void) int tcode; do f tcode -yylex()i printf ("token type td \"%s\"\n", tcode, yytext); ) while (tcode)i return 0; i. Explain the steps needed to convert this source file to an executable program using FLEX under Unix/Linux. ii. Explain what rules 2...6 are supposed to achieve in the above program. (N.B., Rules 2 ...4 are standard FLEX idioms, rules 5 and 6 are not but their meanings should be clear.) ili. The above program is missing some syntax and also contains a number of logical errors. Explain all the errors and rewrite the program so that it is syntactically correct and runs properly iv. Parse the following input string 1.1b1.10b245hi using your rewitten LEX program The instruction set for the stack machine Add [SP-11-SP-1]+[SP): SP ← SP-1 Addition". Pop the top two stack elements, add them and push the Bz 200 Bz (addr) if [SPJ-0 then PC-addr); SP ← SP-1 Example: Add "Branch if equal to Zero". Branch to memory address (addr) if the result back on the stack top of stack is equal to zero, Pop the stack. Bnz (addr) if[SP)メ○then PC ←(addr): SP ← SPー1 Sub Sub Bnz 100 Subtraction". Subtract the top of stack from the next ciement on the stack. Two stack elements are popped and the result is pushed back Muit Branch if not equal to Zero". Branch to memory address (addr) if the top of stack is not equal to zero. Pup the stack. Call (addr SP SP+I: [SP] PC+I: PC+ (addr): "Call a subroutine". First push the address of the instruction follow Mult Call 234 Multiplication". Pop the top two stack elements, multiply thern and push the result back on the stack. ing the Cal1 onto the stack, then jump to (addr). Div Div Ret Ret Return from a subroutine". Pop the top of stack and place its value in the program counter Division". Divide the top of stack by the next element on the stack. Two stack elenents are popped and the result is pushed back. Neg [SP) ←-[SPf Neg "Build Stack Frame". Prepare to enter a subroutine by building the dynamic link portion of a slack frame. Rsf Negation". Negate the top of stack, i.e., replace it with its two's Br 200 Rsf PC -(addr) "Branch to address". Branch to memory address (addr) Remove Stack Frame", Remove a stack frame on exiting a subroa- tine. Restore the Frame Pointer to point to the base of the previous stack frame. Bgz 200 if ISP12 0 then PC +-(addr): SP SP-i "Branch if Greater than or equal to Zero. Branch to memory address (addr) if the top of stack is greater than or equal to zero. Pop the stack Ldp 103 "Load Display Pointer". Copy the old display pointer in (addr) to the location pointed to by the Frame Pointer, then replace it with the current value of the Frame Puinter B4 Bg 200 if (SP]> 0 then PC(adr); SP SP-1 Branch if Greater than zero". Branch to memory address (addr) if the top of stack is greater than zero. Pop the stack. Rdp (addr) Rdp 103 "Restore old Display Pointer". Replace the display pointer currentdy at (addr) with the previously active display pointer, currently pre- served in the location pointed at by the Frame Pointer Blz (addr) Blz 200 if ISP) S 0 then PC(addr): SP SP-1 "Branch if Less than or equal to Zero". Branch to memory address (addr) if the top of stack is less than or equal to zero. Pop the stack. Inc (words) Inc 4 SP SP+(words) Increment the stack pointer". Create (words) words of local vari- able space on the stack Bi 200 if (SPI

Answer 1

Lex source program Lex compiler lex.yy.c lex.yy.c C compiler a.out input a.out tokens

1

i. Save your program under the extension ".l" l stands for lex

the next command to be executed is " flex <programname.l>

for example if your program name is sample.l

then execute flex sample.l

this will create a file lex.yy.c

As the extension indicates it is a 'C ' file

To compile lex.yy.c type gcc lex.yy.c

to run the program ./a.out

ii) rule number 2 is for identifiers it should start with alphabet followed by any number of alphabets or digits

r3- for exponential number with optional sign bit. we can have negative numbers

r4 is for integers with optional negative sign

r5 is for hexadecimal number

r6 is for binary number in the format 0101,1010 but without any decimal point

iii)

%option noyywrap
%{
   #include<stdio.h>
%}
%%
[0-9]               {printf("Valid Identifier");}
-?[0-9]+(\.[0-9]+)?([eE][+|-]?[0-9]+)?            {printf("Valid exponent");}
[0-9a-fA-F]+[hH]       {printf("hex number");}
[01]\.?[01]*[bB]           {printf("binary");}
-?[0-9]+               {printf("number");}
[\t\n]               ;

%%
int main ()
{
int tcode;
do{
tcode= yylex();
printf("enter the value");
printf ("token type %d \"%s\"\n", tcode, yytext);

} while(tcode);
   }

rule for binary has been slightly modified to include '.'

when the input is 1.1b1.10b245hi

what we get is binary binary hex

Valid Identifier 23.9 Ualid exponent .1b1.10b245hi