Wrong code work, why does "else" always work?

Question

Programming

Always after entering data, "else" is triggered, although the file is successfully created and the entered data is entered into it, how to fix it? Maybe the condition is wrong?

#include "stdafx.h"
#include <iostream>
#include <stdio.h>
#include <string.h>

#define FILENM "some.txt"

int main()
{
  FILE* fp = fopen(FILENM, "a");
  puts("What's your name?");
  char name_buf[100];
  fgets(name_buf, 100, stdin);
  puts("What's your birthday?");
  char date_buf[100];
  fgets(date_buf, 100, stdin);
  int name_bytes = fputs(name_buf, fp);
  int bday_bytes = fputs(date_buf, fp);
  if ((name_bytes>0) && (bday_bytes>0)) {
    printf("okay,wrote name and bday to the file %s\n", FILENM);
  }
  else {
    printf("UHHH...You wrong");
  }
  system("pause");
}

Answer 1

Return Value
On success, a non-negative value is returned.
On error, the function returns EOF and sets the error indicator (ferror).
So that's the norm.
Gotta write
if (name_bytes >= 0 && bday_bytes >= 0) {