Unexpected Error ID - not sure why (C++)

Im implementing a C++ program, for project reasons it must be turned in one file so I cannot put what you normally would into a separate header file, it is just at the top of my file. I'm getting this error

project1.cpp:194:12: error: expected unqualified-id OrderOfOps(const std::string& in) ^ project1.cpp:194:12: error: expected ')' project1.cpp:194:11: note: to match this '(' OrderOfOps(const std::string& in)

Here are the lines of code in question: Constructor part which would be a header:

class OrderOfOps
{

public:

    // Constructor
    OrderOfOps(const std::string& in);

private:

    std::string m_inString;


};

Problem Area:

bool IsNumber(const std::string& num)
{
    std::string::const_iterator it = num.begin();

// Look up locale method
while (it != num.end() && std::isdigit(*it, std::locale()))
{
    ++it;
}

return !num.empty() && it == num.end();
}


// Constructor
OrderOfOps(const std::string& in)
{
    m_inString = in;
}