#include<iostream.h>
float temp;

float fn1(float r)
{

    temp=r*r*3.14;
    return temp;
}

float& fn2(float r)
{
    temp=r*r*3.14;
    return temp;
}

int main()
{
    float a=fn1(5.0);
    float& b=fn1(5.0);
    float c=fn2(5.0);
    float& d=fn2(5.0);
    cout<<a<<endl;
    cout<<b<<endl;
    cout<<c<<endl;
    cout<<d<<endl;
}
VC6.0提示：--------------------Configuration: pp193 - Win32 Debug--------------------
Compiling...
ppp193.cpp
F:\C++文件\pp193\ppp193.cpp(7) : warning C4244: '=' : conversion from 'double' to 'float', possible loss of data
F:\C++文件\pp193\ppp193.cpp(13) : warning C4244: '=' : conversion from 'double' to 'float', possible loss of data
F:\C++文件\pp193\ppp193.cpp(20) : error C2440: 'initializing' : cannot convert from 'float' to 'float &'
        A reference that is not to 'const' cannot be bound to a non-lvalue
F:\C++文件\pp193\ppp193.cpp(27) : warning C4508: 'main' : function should return a value; 'void' return type assumed
执行 cl.exe 时出错.

ppp193.obj - 1 error(s), 0 warning(s)
求大神们分析？？？？？？？？？？？？？？？？？？？？？

冤枉我了，我试了这种类型的好多程序都是数据类型不能由“DOUBLE”传到“FLOAT”，都提示这种ERROR，所以我没办法了！