C++ isnan()

The isnan() function returns a number telling whether a given value is a NaN value.

Syntax

isnan(x)

The x parameter is a floating-point value that can be of type float, double, long double, or int. The return value is 1 if x is NaN. Otherwise, 0 is returned.

Note: Common cases of a NaN value include:

• Taking the square root of a negative value
• Dividing positive or negative zero by positive or negative zero (0/0)

Example

In the example below, the isnan() function checks whether or not the value of x is NaN:

#include <iostream>
#include<math.h>
using namespace std;

int main() {
  float x = 0.0 / 0.0;
  cout << "value of isnan(x) is: " << isnan(x) << "\n";
  return 0;
}

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This produces the following output:

value of isnan(x) is: 1

Codebyte Example

In the example below, each possible data type is applied to the isnan() function. The application of the int type involves the sqrt() function:

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