#include<iostream>
using namespace std;
int main()
{
    void swap(int x,int y,int z);
    int x,y,z;
    cout<<"Please enter three number:";
    cin>>x>>y>>z;
    swap(x,y,z);
    return 0;
}
void swap (int &a,int &b,int &c)
{
    int d;
    if (a>b){d=a;a=b;b=d;}
    if(c>b)cout<<a<<" "<<b<<" "<<c<<endl;
    else if(c<a)cout<<a<<"  "<<a<<"  "<<b<<endl;
    else cout<<a<<" "<<c<<" "<<b<<endl;
}

运行结果
Configuration: 1 - Win32 Debug--------------------
Linking...
11.obj : error LNK2001: unresolved external symbol "void __cdecl swap(int,int,int)" (?swap@@YAXHHH@Z)
Debug/1.exe : fatal error LNK1120: 1 unresolved externals
执行 link.exe 时出错.

1.exe - 1 error(s), 0 warning(s)

谢谢各位的点评  我解释一下  我是使用“变量的引用” 我知道把定义的函数放在主函数前在主函数中可以不声明  我就是想知道如果主函数在定义函数前怎么声明