Can not replace word in file using C language

void replace_j(char* oldWord, char* newWord)
{
    printf("without\n");
    printf("%s\n",oldWord);
    printf("%s\n",newWord);
    FILE * fPtr;
    FILE * fTemp;
    FILE* f;
    char path[100];
    char file[BUFFER_SIZE];
    char buff[BUFFER_SIZE];
 //   char oldWord[100], newWord[100];
    f= fopen("files_to_be_scanned.txt", "r");
    while (!feof(f))
    {
    	fgets(file,sizeof(file),f);
       // file[strlen(file) - 1] = '\0';
    	printf("\nfile is %s\n",file);
        strcpy(path,file);
        printf("path is %s\n",path);
        path[strlen(path) - 1] = '\0';
        fPtr  = fopen(path, "r");
        if(fPtr == NULL)
        {
            perror("error");
        }
        fTemp = fopen("replace.tmp", "w");

        /* fopen() return NULL if unable to open file in given mode. */
        if (fPtr == NULL || fTemp == NULL)
        {
            /* Unable to open file hence exit */
            printf("\nUnable to open file.\n");
            printf("Please check whether file exists and you have read/write privilege.\n");
            exit(EXIT_SUCCESS);
        }


        /*
         * Read line from source file and write to destination
         * file after replacing given word.
         */
        while ((fgets(buff, BUFFER_SIZE, fPtr)) != NULL)
        {
            // Replace all occurrence of word from current line
            replaceAll(buff, oldWord, newWord);

            // After replacing write it to temp file.
            fputs(buff, fTemp);
        }


        /* Close all files to release resource */
        fclose(fPtr);
        fclose(fTemp);


        /* Delete original source file */
        remove(path);

        /* Rename temp file as original file */
        rename("replace.tmp", path);

        printf("\nSuccessfully replaced all occurrences of '%s' with '%s'.\n", oldWord, newWord);

    }
}
void replace_with_backup(char* OldWord,char* NewWord)
{


printf("b\n");
    char filename[100];
    int j=0;
    FILE *fptr1, *fptr2;
    //int k=num_files;
    printf("%d\n",num_files);
    while(num_files)
    {
        printf("Enter the filename to open for writing %s\n",buffer[j]);
        scanf("%s", filename);
        fptr1= fopen(buffer[j], "r");
        if (fptr1 == NULL)
        {
            printf("Cannot open file %s \n", filename);
            exit(0);
        }
        // Open another file for writing
        fptr2 = fopen(filename, "w");
        if (fptr2 == NULL)
        {
            printf("Cannot open file %s \n", filename);
            exit(0);
        }
        c = fgetc(fptr1);
        while (c != EOF)
        {
            fputc(c, fptr2);
            c = fgetc(fptr1);
        }
        printf("\nContents copied to %s\n", filename);
        j++;
        num_files--;
    }
    fclose(fptr1);
    fclose(fptr2);
    replace_j(OldWord,NewWord);
}