c++ no suitable constructor exists to convert from "int" to "std::pair<int, int>"

Question

I am having trouble resolving this error. I am not having any luck on Google when I search for this error.

no suitable constructor exists to convert from "int" to "std::pair<int, int>"

#include <utility>

using namespace std;

pair<int, int> solve(int s, int g)
{
    return s % g != 0 ? (-1, -1) : (g, s - g);
}

The error squiggle is under the first s in the return where it is checking...

s % g != 0

I cannot figure out how to resolve this. In C# this would work.

public static (int, int) solve(int s, int g) => s % g != 0 ? (-1, -1) : (g, s - g);

Answer 1

(a, b) is not a pair, it's an expression using the comma operator. It evaluates both the a and the b, but the result of the expression is the b only. That's why it's complaining that it cannot convert your single int into a pair.

For example:

d = (a++, b+=3, c);

will:

• add one to a;
• add three to b; and
• set d to whatever value c has.

If you want an actual pair, you should be using something like std::make_pair(a, b). In your particular case, that would be something like:

return (s % g != 0) ? make_pair(-1, -1) : make_pair(g, s - g);