C rename remove fopen

#include <stdio.h>int main (){    char filename[] = "file.txt";    FILE * fp ;    fp = fopen(filename, "r");    if(fp == NULL)    {      printf("This file NOT exists");          return 0;    }    else    {        fp = fopen(filename, "r");        if(fp == NULL)        {            printf("This file is exists and can not reading \n");           }                  else         {            printf("This file is exists and can reading ");           }    }     int ret;    char oldname[] = "file.txt";    char newname[] = "newfile.txt";    ret = rename(oldname, newname);    if(ret == 0)     {        printf("File renamed successfully\n");    }    else     {        printf("Error: unable to rename the file");    }    fclose(fp);    ret = 0;    ret = remove(newname);    if(ret == 0)     {        printf("File deleted successfully");    }    else     {        printf("Error: unable to delete the file");    }    return(0);}