＃i nclude <iostream.h>

 int &put(int n);

 int vals[10];

 int error=-1;

 void main()

 {

 put(0)=10; //以put(0)函数值作为左值，等价于vals[0]=10;

 put(9)=20; //以put(9)函数值作为左值，等价于vals[9]=20;

 cout<<vals[0];

 cout<<vals[9];

 }

 int &put(int n)

 {

 if (n>=0 && n<=9 ) return vals[n];

 else { cout<<"subscript error"; return error; }

 }