Lexical Analyzer for C Language

Lex.c

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>

int isKeyword(char buffer[]){
  char keywords[32][10] = {"auto","break","case","char","const","continue","default",
                            "do","double","else","enum","extern","float","for","goto",
                            "if","int","long","register","return","short","signed",
                            "sizeof","static","struct","switch","typedef","union",
                            "unsigned","void","volatile","while"};
                            
 int i , flag = 0;
 
 for(int  i = 0 ; i <32 ; i++){
  if(strcmp(keywords[i] , buffer)==0){
    flag = 1;
  }   
 }
 return flag;
}

int main(void) {
  
   FILE *fp;
   fp = fopen("test.c" , "r");
   
   char ch , buffer[15] , ops[] = "*-/+%=" ;
   int i , j = 0;
   
   if(fp == NULL){
     printf("Error opening the FILE.");
     exit(0);
   }
   
   while((ch = fgetc(fp)) != EOF){
     
     for(i = 0 ; i < 6 ; i++){
       if(ch == ops[i]){
         printf("%c is an operator \n" , ch);
       }
     }
    
     if(isalnum(ch)){
       buffer[j++] = ch;
     }
     else if((ch ==" " || ch == "\n") && (j != 0)){
       buffer[j] = "\0";
       j = 0;
       
       if(isKeyword(buffer) == 1){
         printf("%c is a Keyword \n" , buffer);
       }
       else{
         printf("%c is an identifier \n" , buffer);
       }
     }
     
     
     
   }
   
   fclose(fp);
   return 0;
}