关于字符“EOF”的探索

C语言程序设计中有这么一段程序：
#include

/*用于将输入复制到输出的程序；*/
main()
{

        int c;

        while( (c = getchar()) != EOF)
                putchar(c);

}
那么从键盘输入什么的时候字符C才等于EOF呢？

/* This program prompts for input, and then captures a character
 * from the keyboard. If EOF is signalled (typically through a
 * control-D or control-Z character, though not necessarily),
 * the program prints 0. Otherwise, it prints 1.
 *
 * If your input stream is buffered (and it probably is), then
 * you will need to press the ENTER key before the program will
 * respond.
 */
 
#include
 
int main(void)
{
  printf("Press a key. ENTER would be nice :-)\n\n");
  printf("The expression getchar() != EOF evaluates to %d\n", getchar() != EOF);
  return 0;
}

由以上可知输入control-D时，C ==  EOF！
那么EOF的值又是多少呢？

/*Write a program to print the value of EOF .*/
#include
 int main(void)
{
  printf("The value of EOF is %d\n\n", EOF);
 
  return 0;
}
由以上程序结果可知EOF = -1 。