What is EOF in the C programming language?

Using below program, i explained "How to EOF is working in programming language?"
#include 
main(){
	long number_of_character;
	number_of_character=0;
	clrscr();
	while(getchar()!=EOF)
		++number_of_character;
	printf("%d\n",number_of_character);

	getch();
}
When i compile this program I will the get the count of input characters. EOF is equal to CTRL+Z for Windows EOF is equal to CTRL+D for Windows [caption id="attachment_1531" align="aligncenter" width="641"]Characters Count C Program Characters Count C Program[/caption]