使用VC6打开考生文件夹下的工程test40_1，此工程包含一个源程序文件test40_1.cpp，但该程序运行有问题，请改正函数中的错误，使该程序的输出结果为：

The first result is 5

The second result is 2

The third result is 2

The fourth result is 6

源程序文件test40_1.cpp清单如下：

include ＜iostream.h＞

int subtraction (int a, int b)

{

int r;

r=a-b;

/***************** found ************************/

return &r;

}

int main ()

{

int x=5, y=3, z;

z = subtraction (7,2);

cout ＜＜ "The first result is "＜＜ z ＜＜ '\n';

cout ＜＜ "The second result is "＜＜ subtraction(7,subtraction (7,2)) ＜＜ '\n';

/**************** found *************************/

cout ＜＜ "The third result is "＜＜ subtraction (&x,&y) ＜＜ '\n';

/***************** found ************************/

z= 4 + *subtraction (x,y);

cout ＜＜ "The fourth result is "＜＜ z ＜＜ '\n';

return 0;

}