I try this way and good fail many time. Any help, will be celebrate with grate appreciation. Thanks. I also try fgets() same way but didn't work as well.
int line_count ()
{
    FILE * fp;         // file open from here.
    int i=0;
    int c;
    if ((fp = fopen ("file.txt", "a")) != NULL){
        while ((c=fgetc(fp))!=EOF)
        {
            if (c=='\n') {
                i++;
            }
           
        }
        fclose(fp);
    }
    else printf(" Error.\n");
    return i;
}