C++ program for checking whether the input is a leap year - c++

Question

I am Tony and I am new to c++ programming. I would like to ask a question related to creating a program to check for leap year.
In the following codes, I try to create a bool function to check whether the input is a leap year. If the input is negative, I will cout "Bye!" and stop the program immediately. If the input is positive, then I will check whether it is a leap year using the bool function I built until the input is a negative number then I will exit the program.
However, I am not able to find what mistakes I have made and the current situation is, when I input a positive value, there is no result generated. Please help if you are available. Much thanks to you. : )
#include <iostream>
#include <cmath>
#include <string>
#include <iomanip>
using namespace std;
bool leap_year(int year);
int main()
{
int year;
while (cout << "Enter a year (or negative number to quit): ")
{
cin >> year;
if (leap_year(year) == false && year <0 )
{
cout << "Bye!" << endl;
}
break;
if (leap_year(year) == false && year >0 )
{
cout << "The year is not a leap year." << endl;
}
if (leap_year(year) == true && year >0 )
{
cout << "The year is a leap year." << endl;
}
return 0;
}
}
bool leap_year(int year)
{
bool is_leap_year = false;
if (year % 4 == 0)
{
is_leap_year = true;
}
if (year % 100 == 0)
{
is_leap_year = false;
}
if (year % 400 == 0)
{
is_leap_year = true;
}
return is_leap_year;
}

Answer 1

First of all, you (should) want a while(true) loop and not a while(std::ostream) loop.
So replace
while (cout << "Enter a year (or negative number to quit): ")
{
with
while (true)
{
cout << "Enter a year (or negative number to quit): ";
As #paddy pointed out, you can check std::ostream`s return type to look for errors when printing out. But in this simple program I doubt it's necessary.
Then you have the break outside your if statement, which will always break out of the program (no matter the Input). Replace
if (leap_year(year) == false && year <0 )
{
cout << "Bye!" << endl;
}
break;
with
if (year < 0)
{
cout << "Bye!" << endl;
break;
}
(there's no need to check if the negative input is a leap year. You can achieve entering only 1 if-statement with if-else statments, therefore you can also replace if(leap_year(year) == false && year < 0) with just if (year < 0); as I did.)
When you apply this to all statements (not changing their internal logic) and remove the return 0; at the end of the loop, you get your desired program flow. Also removing using namespace std; is just better (read here why). You also don't Need to include <iomanip>, <cmath> nor <string>. Full Code:
#include <iostream>
bool leap_year(int year);
int main() {
int year;
while (true) {
std::cout << "Enter a year (or negative number to quit): ";
std::cin >> year;
if (year < 0) {
std::cout << "Bye!" << std::endl;
break;
}
else if (leap_year(year)) {
std::cout << "The year is a leap year." << std::endl;
}
else {
std::cout << "The year is not a leap year." << std::endl;
}
}
}
bool leap_year(int year){
bool is_leap_year = false;
if (year % 4 == 0){
is_leap_year = true;
}
if (year % 100 == 0){
is_leap_year = false;
}
if (year % 400 == 0){
is_leap_year = true;
}
return is_leap_year;
}