LEXRER

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

int main(int argc, char const *argv[])
{
    char ch,buffer[100],operators[]="+.*/%=";
    FILE *fp;
    int i,j=0;

    // open the source file given in first argument
    if(argc != 2)
        printf("Source file is not provided.\n");

    fp=fopen(argv[1],"r");

    //if can't open file throw error
    if(fp==NULL)
    {
        printf("Error while opening the file\n");
        exit(2);
    }

    int fl=1, cnt=1;
    //parse the file, one by one character
    while((ch=fgetc(fp))!=EOF){

        //check if the char is a operator
        for(i=0;i<6;i++)
        {
            if(ch==operators[i])
            {
                printf("%c is operator\n",ch);
                if(!fl)buffer[j++]=',';
                fl=1;
            }
        }
        // cehck is the char is alphanumeric
        if(isalnum(ch))
        {
            buffer[j++]=ch;
            fl=0;
        }
        else if((ch=='\n')&& j!=0)
        {
            buffer[j]='\0';
            j=0;
            printf("%s is identifier\n",buffer);
            fl=1;
            printf("Above tokens are from line %d \n",cnt);

            // if the current char is a newline increase the newline counter
            if( ch == '\n')
                cnt++;
        }
    }

    fclose(fp);

    return 0;
}