Question

How to check if a double is NaN in C++

Answer 1

#include <iostream>
#include <cmath> // For std::isnan

int main() {
    double d = std::nan(""); // Example NaN value

    if (std::isnan(d)) {
        std::cout << "The value is NaN." << std::endl;
    } else {
        std::cout << "The value is not NaN." << std::endl;
    }
}

 
 
/*
run:
 
The value is NaN.
 
*/
   

 

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Answer 2

#include <iostream>
#include <cmath> // For std::isnan

int main() {
    double d = std::nan(""); // Example NaN value

    if (d != d) {
        std::cout << "The value is NaN." << std::endl;
    } else {
        std::cout << "The value is not NaN." << std::endl;
    }
}

 
 
/*
run:
 
The value is NaN.
 
*/

 

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