DEVELOP A LEXICAL ANALYZER TO RECOGNIZE A FEW PATTERNS IN C( WITH OUTPUT)

December 04, 2017

AIM:
To develop a lexical analyzer to identify identifiers, constants, comments, operators etc using C program

ALGORITHM:
Step1: Start the program.
Step2: Declare all the variables and file pointers.
Step3: Display the input program.
Step4: Separate the keyword in the program and display it.
Step5: Display the header files of the input program
Step6: Separate the operators of the input program and display it.
Step7: Print the punctuation marks.
Step8: Print the constant that are present in input program.
Step9: Print the identifiers of the input program.

PROGRAM CODE:

//Develop a lexical analyzer to recognize a few patterns in C.

#include<string.h>
#include<ctype.h>
#include<stdio.h>
#include<stdlib.h>
void keyword(char str[10])
{
if(strcmp("for",str)==0||strcmp("while",str)==0||strcmp("do",str)==0||strcmp("int",str)==0||strcmp("float",str)==0||strcmp("char",str)==0||strcmp("double",str)==0||strcmp("printf",str)==0||strcmp("switch",str)==0||strcmp("case",str)==0)
  printf("\n%s is a keyword",str);
else
  printf("\n%s is an identifier",str);
}
void main()
{
FILE *f1,*f2,*f3;
char c,str[10],st1[10];
int num[100],lineno=0,tokenvalue=0,i=0,j=0,k=0;
f1=fopen("input","r");
f2=fopen("identifier","w");
f3=fopen("specialchar","w");
while((c=getc(f1))!=EOF)
{
  if(isdigit(c))
  {
  tokenvalue=c-'0';
  c=getc(f1);
  while(isdigit(c))
  {
   tokenvalue*=10+c-'0';
   c=getc(f1);
  }
  num[i++]=tokenvalue;
  ungetc(c,f1);
  }
  else
  if(isalpha(c))
  {
   putc(c,f2);
   c=getc(f1);
   while(isdigit(c)||isalpha(c)||c=='_'||c=='$')
   {
    putc(c,f2);
    c=getc(f1);
   }
   putc(' ',f2);
   ungetc(c,f1);
  }
  else
  if(c==' '||c=='\t')
  printf(" ");
  else
  if(c=='\n')
  lineno++;
  else
  putc(c,f3);
}
fclose(f2);
fclose(f3);
fclose(f1);
printf("\n the no's in the program are:");
for(j=0;j<i;j++)
  printf("\t%d",num[j]);
printf("\n");
f2=fopen("identifier","r");
k=0;
printf("the keywords and identifier are:");
while((c=getc(f2))!=EOF)
if(c!=' ')
str[k++]=c;
else
{
  str[k]='\0';
  keyword(str);
  k=0;
}
fclose(f2);
f3=fopen("specialchar","r");
printf("\n Special Characters are");
while((c=getc(f3))!=EOF)
printf("\t%c",c);
printf("\n");
fclose(f3);
printf("Total no of lines are:%d",lineno);
}

OUTPUT: