c++ - How do I call a function from another .cpp file into the file where my int main() is? -

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so program requires me make function in 1 file, , call another.

i have 1 file called convertdays.cpp this:

#include <iostream>  int convertdays(int, int, int);   int convertdays(int month, int day, int year) { int date;  date = year * 1000 + month * 100 + day;  return date; } 

then have file int main() stuff is, this:

#include <iostream> using namespace std;   int main() { int day, month, year;   cout << "please enter month: " << endl;  cin >> month;   cout << "please enter day: " << endl; cin >> day;   cout << "please enter year: " << endl;  cin >> year;   convertdays(month, day, year); //convertdays stays in red though.  //still need add couple of more things not necessary right now.  system("pause");  return 0;  } 

how make work can keep of functions in file , call them in when need them?

make file called "convertdays.h", containing function declaration:

int convertdays(int, int, int);  

this called header file.

then @ top of main.cpp:

#include "convertdays.h" 

(it's idea put same thing @ top of convertdays.cpp, though not strictly necessary.)

then when build executable, link main.o , convertdays.o.