===== lex_anal.c =====

#include<stdio.h> 
#include<ctype.h> 
#include<string.h> 
int main(){ 
 FILE *input,*output; 
 int l=1; 
 int t=0; 
 int j=0; 
 int i,flag; 
 char ch,str[20]; 
 input = fopen("input.txt","r"); 
 output = fopen("output.txt","w"); 
 char keyword[30][30] = {"int","main","if","else","do","while"}; 
 fprintf(output,"Line no. \t Token no. \t\t Token \t\t Lexeme\n\n"); 
 while(!feof(input)) 
 { 
  i=0; 
  flag=0; 
  ch=fgetc(input); 
  if( ch=='+' || ch== '-' || ch=='*' || ch=='/' ){ 
   fprintf(output,"%7d\t\t %7d\t\t Operator\t %7c\n",l,t,ch); 
   t++; 
  } 
  else if( ch==';' || ch=='{' || ch=='}' || ch=='(' || ch==')' || ch=='?' || ch=='@' ||ch=='!' || ch=='%'){ 
   fprintf(output,"%7d\t\t %7d\t\t Special symbol\t %7c\n",l,t,ch); 
   t++; 
  } 
  else if(isdigit(ch)){ 
   fprintf(output,"%7d\t\t %7d\t\t Digit\t\t %7c\n",l,t,ch); 
   t++; 
  } 
  else if(isalpha(ch)){ 
   str[i]=ch; 
   i++; 
   ch=fgetc(input); 
   while(isalnum(ch) && ch!=' '){ 
    str[i]=ch; 
    i++; 
    ch=fgetc(input); 
   } 
   str[i]='\0'; 
   for(j=0;j<=30;j++){ 
    if(strcmp(str,keyword[j])==0){ 
     flag=1; 
     break; 
    } 
   } 
   if(flag==1){ 
    fprintf(output,"%7d\t\t %7d\t\t Keyword\t %7s\n",l,t,str); 
    t++; 
   } 
   else{ 
    fprintf(output,"%7d\t\t %7d\t\t Identifier\t %7s\n",l,t,str); 
    t++; 
   } 
  } 
  else if(ch=='\n'){ 
   l++; 
  } 
 } 
 fclose(input); 
 fclose(output); 
 return 0; 
}

===== input.txt =====
#include<stdio.h>
void main()
{
 printf("Hello World");
}

===== run =====
nano lex_anal.c
gcc lex_anal.c -o lex_anal
./lex_anal
cat output.txt