1.#QNAN错误C++

Question

我是个编程新手，正在尝试写一个新的程序。在检查我的程序时，它返回了错误代码1.#QNAN。我试着隔离变量并研究答案，但找不到任何解决方案。

我的代码：

 // This is a program to decide what culvert should be properly used for a specific installation
// using given measurements and data
//
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>

using namespace std;
// initializing functions 
double slope_function();
double cbasin();
// initializing classes: Subdivisions specs

//intitializing global variables
double edge_road =0;
double up_stream  =0;
double down_stream =0;
double tbm =0.0;

//double culv_length =0;
double slope = 0.0 ;
char street_name[1001];
int min_culv = 15;
double up_strm_culv =0;
double dwn_strm_culv =0;


int main (int nNumberofArgs, char* pszArgs[])
{
    cout<< "This program will allow the surveyor to double check their calculations\n";
    cout << "in deciding what size, type, and requirements are allowed for the\n";
    cout << "installation of culverts in Terrebonne Parish.\n\n";



// begin input
   cout << "what is the name of the street\nwhere the culverts will be installed: ";
   cin.getline (street_name,1000);
   cout << endl;
   cout << "What is the Benchmark: ";
   cin >> tbm;
   cout << endl;
   cout << "What is the elevation of the edge of the road: ";
   cin >> edge_road;
   cout << endl;
   cout << "What is the up-stream culvert size: ";
   cin >> up_strm_culv;
   cout << endl;
   cout << "What is the culverts up-stream inverted elevation: ";
   cin >> up_stream;
   cout << endl;
   cout << "What is the down-stream culvert size: ";
   cin >> dwn_strm_culv;
   cout << endl;
   cout << "What is the culverts down-stream inverted elevation: ";
   cin >> down_stream;
   cout << endl;
   cout << "What is the length of culvert requested: ";
   cin >> culv_length;


   cout << "Your slope is : "; 
   cout << slope_function();
   cout << endl;
   cout << street_name;
   cout << endl;
   cout << cbasin();


    cout << endl;
  // wait until user is ready before terminating program
  // to allow the user to see the program results 
  system ("pause");
  return 0;
}  

// slope function 
double slope_function()
{
    double riseoverrun = 0.0;
    slope = (up_stream - down_stream)/ culv_length;
    return slope;
}


// Catch Basin function
double cbasin ( )
{
    double cb = 0;
    cb = culv_length / 60;
    cout << endl;
    cout << "You need ";
   cout << cb;
   cout << " catch basins for this job.";
   cout << endl;
}

Answer 1

1#QNAN是"quiet NAN“的字符串表示。"NAN“是”非数字“，仅适用于浮点数和双精度数。

NANs实际上对于表示"null“值非常有用(而不是挑选一些真正的数字，然后希望你不需要那个数字作为它的自然含义)。

如果某些数学运算“无效”(例如，取负数的对数)，则可能会返回NAN。

您可以使用以下命令从C++生成QNAN

double d = std::numeric_limits<double>::quiet_NaN();

NAN上的任何比较操作(==、<=等)都返回false，即使将其等价性与其自身进行比较也是如此，除了!=，它总是返回true (即使与自身进行比较)。

(代码中的实际bug似乎是一个返回double但没有return语句的函数)。