/*Lexical Analyser Using C
Program */
#include<stdio.h>
#include<string.h>
char str[50];
int st;
char c;
void main(int argc,char *argv[])
{
FILE *ptr;
int l,i,j,f,k;
f=0;
char
key[50][50]={"int","for","do","while","if","char","float","double","case","struct","void","switch","else","return","break"};
char
sps[50][50]={"[","]","{","}","(",")","#",";","\\","'","\"",".","!","?"};
char
op[50][50]={"&&","<",">","||","=","+","-","*","/","%"};
char
fs[50][50]={"%d","%s","%f","%c"};
char
escp[50][50]={"\n","\t","\b","\\n","\\t","\\a","\\b"};
if(argc!=2)
printf("Invalid
argument list\n");
else
if((ptr=fopen(argv[1],"r"))==NULL)
printf("File is
Empty\n");
else
{
c=fgetc(ptr);
while(feof(ptr)!=1)
{
st=0;
str[0]=c;
for(i=1;str[i]!='\n';i++)
{
c=fgetc(ptr);
if(c=='\n')
break;
str[i]=c;
}
str[i]='\0';
puts(str);
k=0;
for(i=0;i<50;i++)
{
if(strcmp(str,key[i])==0)
{
printf("The
string is a keyword\n");
k=1;
break;
}
else if(strcmp(str,sps[i])==0)
{
printf("The
string is a special charactor\n");
k=1;
break;
}
else
if(strcmp(str,op[i])==0)
{
printf("The
string is an operator\n");
k=1;
break;
}
else
if(strcmp(str,fs[i])==0)
{
printf("The
string is an format specifiers\n");
k=1;
break;
}
else
if(strcmp(str,escp[i])==0)
{
printf("The
string is an escape sequence\n");
k=1;
break;
}
}
if(k==0)
{
l=strlen(str);
for(i=0;i<l;i++)
{
if(st==0)
{
if((str[i]>=65&&str[i]<=90)||(str[i]>=97&&str[i]<=122)||(str[i]==95))
{st=1;l--;}
else
if(str[i]>=49&&str[i]<=57)
st=2;
else
if((str[i]==48&&str[i+1]==46)||(str[i]==46))
{
st=3;
i++;
}
else
st=4;
}
else if(st==1)
{
if((str[i]>=65&&str[i]<=90)||(str[i]>=97&&str[i]<=122)||(str[i]>=48&&str[i]<=57)||(str[i]==95))
st=1;
else
st=4;
}
else if(st==2)
{
if(str[i]>=48&&str[i]<=57)
st=2;
else if((str[i]==46))
st=3;
else
st=4;
}
else if(st==3)
{
if(str[i]>=49&&str[i]<=57)
st=3;
else if(str[i]==48)
{
for(j=i+1;j<l;j++)
{
if(str[j]!=48)
st=3;
else
st=4;
}
}
else
st=4;
}
else
{
if(str[i]>=48&&str[i]<=57)
st=4;
else
st=4;
}
}
if(st==1)
printf("The
string is a valid Identifier\n");
else if(st==2)
printf("The
string is a valid number\n");
else if(st==3)
printf("The
string is a valid floating point number\n");
else
printf("The
string is an invalid token\n");
}
c=fgetc(ptr);
}
}
}
File
manju
while do int float
1.3565
1334
\n
}
/
%d
\t
5gf
Output
manju
The string is a valid Identifier
while
The string is a keyword
1.3565
The string is a valid floating point number
1334
The string is a valid number
\n
The string is an escape sequence
}
The string is a special charactor
/
The string is an operator
%d
The string is an format specifiers
\t
The string is an escape sequence
5gf
The string is an invalid token
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