c++ - error: cannot convert `double ()(double) throw ()' to `double' in assignment -

can't figure out why have these error messages. brand new c++.

payroll.cpp: in function `void fgross()': payroll.cpp:57: error: assignment of function `double round(double)' payroll.cpp:57: error: cannot convert `double' `double ()(double) throw ()' in assignment payroll.cpp:59: error: cannot convert `double ()(double) throw ()' `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' `double ()(double) throw ()' in assignment payroll.cpp:67: error: cannot convert `double ()(double) throw ()' `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' `double ()(double) throw ()' in assignment payroll.cpp:75: error: cannot convert `double ()(double) throw ()' `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' `double ()(double) throw ()' in assignment payroll.cpp:84: error: cannot convert `double ()(double) throw ()' `double' in assignment payroll.cpp: in function `void fround()': payroll.cpp:110: error: invalid operands of types `double ()(double) throw ()' , `double' binary `operator+' 

this code:

#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 <<"\n\n\t\twelcome payroll program!!!\n\n\n";           cout <<"how many hours did work week?\t";         cin >> hours;         cout <<"how many children have?";         cin >> ins;          fgross();         fsoc();         ffed();         fst();         funin();         fnet ();           cout <<"payroll stub:\n\n\t"              <<"hours:\t" << hours              <<"\n\trate:\t" << rate <<"16.78 $/hr\n\t"              <<"gross:\t" << d << gross              <<"\n\n\tsocsec:\t" << d << socsec              <<"\n\tfedtax:\t" << d << fedtax              <<"\n\tsttax:\t" << d << sttax              <<"\n\tunion:\t" << d << unin;          fins();          cout <<"\n\tnet:\t" << net <<"\n\nthank using pp!!"              <<"\n\nendeavor have 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 << "\n\tins:\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;   } 

there standard library function named round, declared in <cmath>. code expects global variable named round, appear have forgotten declare, of uses of round in fgross, fsoc, etc resolve function. can't assign function name, , can't assign pointer-to-function (which when use function name on right-hand side of assignment) floating-point variable. hence confusing errors.

in order make program work, need change name of variable round; if add missing declaration, error,

test.cc:10:12: error: ‘double round’ redeclared different kind of symbol /usr/include/x86_64-linux-gnu/bits/mathcalls.h:326:1: note:     previous declaration ‘double round(double)’ 

... @ least give more of clue problem is.

there lot of other problems code, of point out important three:

• all of f-functions should take arguments , return value; of global variables should removed. (i suspect near-literal translation of cobol, that's next refactor plan do, must point out anyway.)
• computations on money must done using fixed-point arithmetic avoid rounding , underflow problems; simplest thing, work enough kind of program, scale integer number of cents , use int64_t variables; in computations involving interest compounded on many years, or similar, might want scale 100ths or 1000ths of cent instead.
• using namespace std bad practice , cause more problems of type tripped over. write using std::foo; each foo need.