错误：无法在赋值中将"双 ()(双)抛出 ()"转换为"双倍"

无法弄清楚为什么我有这些错误消息。我是C++的新手。

payroll.cpp: In function `void fGross()':
payroll.cpp:57: error: assignment of function `double round(double)'
payroll.cpp:57: error: cannot convert `double' to `double ()(double)
throw ()' in assignment
payroll.cpp:59: error: cannot convert `double ()(double) throw ()'
to `double' in assignment
payroll.cpp: In function `void fSoc()':
payroll.cpp:65: error: assignment of function `double round(double)'
payroll.cpp:65: error: cannot convert `double' to `double ()(double)
throw ()' in assignment
payroll.cpp:67: error: cannot convert `double ()(double) throw ()'
to `double' in assignment
payroll.cpp: In function `void fFed()':
payroll.cpp:73: error: assignment of function `double round(double)'
payroll.cpp:73: error: cannot convert `double' to `double ()(double)
throw ()' in assignment
payroll.cpp:75: error: cannot convert `double ()(double) throw ()'
to `double' in assignment
payroll.cpp: In function `void fSt()':
payroll.cpp:82: error: assignment of function `double round(double)'
payroll.cpp:82: error: cannot convert `double' to `double ()(double)
throw ()' in assignment
payroll.cpp:84: error: cannot convert `double ()(double) throw ()'
to `double' in assignment
payroll.cpp: In function `void fround()':
payroll.cpp:110: error: invalid operands of types `double ()(double)
throw ()' and `double' to binary `operator+'

这是我的代码：

#include <iostream>
#include <climits>
#include <cmath>
using namespace std;
double hours, gross, socSec, fedTax, stTax, ins, net;
double const rate = 16.78;
double unin = 10.00;
char d = '$';
void fGross();
void fSoc();
void fFed();
void fSt();
void fUnin();
void fIns();
void fNet();
void fround();

int main (void)
{
cout <<"nnttWelcome to the Payroll Program!!!nnn"; 
cout <<"How many hours did you work this week?t";
cin >> hours;
cout <<"How many children do you have?";
cin >> ins;
fGross();
fSoc();
fFed();
fSt();
fUnin();
fNet (); 
cout <<"Payroll Stub:nnt"
<<"Hours:t" << hours
<<"ntRate:t" << rate <<"16.78 $/hrnt"
<<"Gross:t" << d << gross
<<"nntSocSec:t" << d << socSec
<<"ntFedTax:t" << d << fedTax
<<"ntStTax:t" << d << stTax
<<"ntUnion:t" << d << unin;
fIns();
cout <<"ntNet:t" << net <<"nnThank you for using the PP!!"
<<"nnEndeavor to have a StarTrek-esque day!";
return 0;
}    

void fGross()
{
round = rate * hours;
fround();
gross = round;
return;
}
void fSoc()
{
round = gross * .06;
fround();
socSec = round;
return;
}
void fFed()
{
round = gross * .14;
fround();
fedTax = round;
return;
}
void fSt()
{
round = gross * .05;
fround();
stTax = round;
return;
}
void fIns()
{
if (ins >= 3)
{
ins = 35.00;
cout << "ntIns:t" << d << ins;
}
else
{
ins = 0.00;
}
return;
}
void fNet()
{
net = gross - socSec - fedTax - stTax - unin - ins;
return;
}
void fround()
{
round = floor((round + .05) * 100);
return;  
}