[Term Entry] C++ Math-functions: isunordered() #8022

Author: abey1

content/cpp/concepts/math-functions/terms/isunordered/isunordered.md

@@ -0,0 +1,76 @@
+---
+Title: 'isunordered()'
+Description: 'Returns true if one or both of the arguments is a NaN value'
+Subjects:
+  - 'Computer Science'
+Tags:
+  - 'Arithmetic'
+  - 'Functions'
+  - 'Numbers'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+When comparing two floating-point numbers, the comparison behaves as unordered if one of them is a `NaN` (Not a Number). The function **`isunordered()`** receives two floating-point numbers and checks if either of them is a `NaN`. `isunordered()` returns `true` if one or both of the arguments is `NaN`, and returns `false` only if both arguments are normal floating-point numbers. 
+
+## Syntax
+
+```pseudo
+isunordered(a, b)
+```
+The function `isunordered(a, b)` receives two arguments `a` and `b`, of type `double`, `float`, or `long double` data types and returns `true` if either `a` or `b` is `NaN`. It will return `false` only if both `a` and `b` are normal floating-point numbers. 
+
+## Example
+
+```cpp
+#include <iostream>
+#include <cmath>
+using namespace std;
+
+int main()
+{
+	cout << (isunordered(3.0, NAN)?"true":"false") << endl;
+		// returns true
+	cout << (isunordered(NAN, 3.0)?"true":"false") << endl;
+		// returns true
+	cout << (isunordered(NAN, 3.0)?"true":"false") << endl;
+		// returns true
+	cout << (isunordered(3.0, 4.0)?"true":"false") << endl;
+		// returns false 
+}
+```
+
+## Codebyte Example
+
+The following example is runnable and shows what the function `isunordered()` resolves to, when given different kinds of arguments. In the example the helper function `checkNaN()` takes in two double arguments `a` and `b` and passes them to `isunordered()` and outputs the appropriate message depending on the condition `isunordered()` returns. the `main()` function calls `checkNaN()` multiple times with different arguments. For simplicity, `checkNaN()` only takes arguments with `double` data type. 
+
+```codebyte/cpp
+#include <iostream>
+#include <cmath>
+using namespace std;
+
+void checkNaN(double a, double b) {
+	if (isunordered(a, b))
+		cout << a << " is NOT comparable with " << b << endl;
+	else
+		cout << a << " is comparable with " << b << endl;
+}
+
+
+int main()
+{
+	double nan = NAN; // a NaN (Not a Number) value
+	double pi = 3.14; // a regular double number
+	double c = 2.99792458e8; // a regular double number
+
+	checkNaN(nan, nan); 
+	// outputs: nan is NOT comparable with nan
+	checkNaN(nan, pi);
+	// outputs: nan is NOT comparable with 3.14
+	checkNaN(c, nan);
+	// outputs: 2.99792e+08 is NOT comparable with nan
+	checkNaN(c, pi);
+	// outputs: 2.99792e+08 is comparable with 3.14
+}
+```