c++ double is nan

First, let's consider that NaN stands for "not a number" and is used to represent undefined or unrepresentable values in floating-point calculations. In C++, the double data type is used to represent double-precision floating-point numbers. When a double variable is assigned a value that results in a NaN, it indicates that the result of the operation is not a valid number. This can happen, for example, when dividing zero by zero, taking the square root of a negative number, or performing other invalid operations on floating-point numbers. When a double variable is set to NaN, it means that the result of the operation cannot be represented as a valid number.