奇怪的现象

我在Visual C++ 6.0编译器中遇到了这样的问题:
#include "iostream.h"
#include "stdio.h"
void main()
{
cout<<"This is C++ program ";
printf("This is C program ");
}

输出结果是:
This is C program This is C++ program

#include "iostream.h"
#include "stdio.h"
void main()
{
cout<<"This is C++ program "<<endl;
printf("This is C program ");
}
输出结果是:
This is C++ program
This is C program
这是怎么回事啊?