Quick Answer

Attempting to use undefined operators on types

Understanding the Issue

This error occurs when trying to use an operator on types that don't support it, either built-in types used incorrectly or custom types without operator overloads.

The Problem

This code demonstrates the issue:

Cpp Error 
// Problem: No << operator
struct Point { int x,y; };
Point p;
std::cout << p; // Error

The Solution

Here's the corrected code:

Cpp Fixed 
// Solution: Overload operator
std::ostream& operator<<(std::ostream& os, const Point& p) {
    return os << "(" << p.x << "," << p.y << ")";
}

Key Takeaways

Implement operator overloads for custom types when needed.