Linux C IO question: ctrl+D once or twice? [duplicate]

test1.c

#include <stdio.h>

int main(void)
{
    int ch;
    FILE *fp;
    fp = fopen("file1.txt", "w");

    while ((ch = fgetc(stdin)) != EOF)
    {
        fputc(ch, fp);
    }

    printf("\n");

    return 0;
}

test2.c

#include <stdio.h>

int main(void)
{
    int ch;

    while ((ch = fgetc(stdin)) != EOF)
    {
        fputc(ch, stdout);
    }

    printf("\n");

    return 0;
}

The difference between the two files is the expression inside the while loop(one outputs to a file while another outputs to stdout).

The behavior of two program confuses me.

test1.c: I should type twice ctrl+D to complete my input. For example I type "123 ctrl+D ctrl+D", the first fgetc return and while loop run and finally ch can get EOF to run out of while loop.

test2.c: The fgetc return when I type ctrl+D just once. For example "123 ctrl+D", The fgetc return and while loop run but ch can not get EOF so it's blocked by the last fgetc.

Why?

My environment:

gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0
Linux ubuntu 4.15.0-76-generic #86-Ubuntu SMP x86_64 GNU/Linux