c++ - Pointer to function -

what mistakes mean? why when make types double, doesn't show same mistakes?

c2556 'int div(int,int)': overloaded function differs return type 'div_t div(int,int)'
c2371 'div': redefinition; different basic types
c2491 'div': definition of dllimport function not allowed
c2664 'int calculate(int,int,int (__cdecl *)(int,int))': cannot convert argument 3 'overloaded-function' 'int (__cdecl *)(int,int)'

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#include <iostream> using namespace std;  int sum(int x, int y) {     return x + y; }  int subs(int x, int y) {     return x - y; }  int mult(int x, int y) {     return x * y; }  int div(int x, int y) {     return x / y; } int calculate(int x, int y, int(*func)(int, int)) {     return func(x, y); } void main() {     cout<<"sum:"<< calculate(8, 4, sum)<<endl;     cout << "subs:" << calculate(8, 4, subs) << endl;     cout << "mult:" << calculate(8, 4, mult) << endl;     cout << "div:" << calculate(8, 4, div) << endl; } 

there exists div function in stdlib.h standard header included iostream, overload in conflict with.

one way use own namespace (using namespaces idea), this:

#include <iostream>  namespace {       int sum(int x, int y) {     return x + y;   }         int subs(int x, int y) {     return x - y;   }         int mult(int x, int y) {     return x * y;   }        int div(int x, int y) {     return x / y;   }   int calculate(int x, int y, int(*func)(int, int)) {     return func(x, y);   } }  int main() {   std::cout << "sum:"  << my::calculate(8, 4, my::sum)  << std::endl;   std::cout << "subs:" << my::calculate(8, 4, my::subs) << std::endl;   std::cout << "mult:" << my::calculate(8, 4, my::mult) << std::endl;   std::cout << "div:"  << my::calculate(8, 4, my::div)  << std::endl;   return 0; } 

of course can use shorter alternative using:

... namespace { ... } using my; ...   std::cout << "sum:"  << my::calculate(8, 4, sum)  << std::endl;   std::cout << "subs:" << my::calculate(8, 4, subs) << std::endl;   std::cout << "mult:" << my::calculate(8, 4, mult) << std::endl;   std::cout << "div:"  << my::calculate(8, 4, my::div)  << std::endl; // scoped eliminate ambiguity