[Term Entry] C++ Math-functions: islessequal()

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

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+---
+Title: 'islessequal()'
+Description: 'Checks whether the first floating-point value is less than or equal to the second, without raising floating-point exceptions.'
+Subjects:
+  - 'Computer Science'
+  - 'Game Development'
+Tags:
+  - 'Arithmetic'
+  - 'Functions'
+  - 'Math'
+  - 'Numbers'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+The **`islessequal()`** function compares two floating-point values and returns `true` if the first value is less than or equal to the second. It performs a quiet comparison, meaning it does not raise floating-point exceptions and always returns `false` if either value is `NaN`.
+
+This function is provided by the `<cmath>` header and is safer than using the `<=` operator when working with floating-point edge cases.
+
+## Syntax
+
+```pseudo
+islessequal(x, y)
+```
+
+**Parameters:**
+
+- `x`: The first numeric value to compare.
+- `y`: The second numeric value to compare.
+  Both parameters can be floating-point or integer types due to overloads.
+
+**Return value:**
+
+- Returns `true` if `x` is less than or equal to `y` and neither value is `NaN`.
+- Returns `false` otherwise, including when either argument is `NaN`.
+
+## Example 1: Comparing two numeric values
+
+In this example, `islessequal()` is used to compare two regular numeric values:
+
+```cpp
+#include <iostream>
+#include <cmath>
+using namespace std;
+
+int main() {
+  double a = 4.5;
+  double b = 7.2;
+
+  cout << boolalpha;
+  cout << islessequal(a, b) << endl;
+  cout << islessequal(b, a) << endl;
+
+  return 0;
+}
+```
+
+The output of this code is:
+
+```shell
+true
+false
+```
+
+## Example 2: Comparison involving `NaN`
+
+In this example, `islessequal()` safely handles a comparison involving `NaN`:
+
+```cpp
+#include <iostream>
+#include <cmath>
+using namespace std;
+
+int main() {
+  double x = 5.0;
+  double y = NAN;
+
+  cout << boolalpha;
+  cout << islessequal(x, y) << endl;
+  cout << islessequal(y, x) << endl;
+
+  return 0;
+}
+```
+
+The output of this code is:
+
+```shell
+false
+false
+```
+
+## Codebyte Example
+
+In this example, `islessequal()` is used inside a helper function to check ordering between different numeric inputs:
+
+```codebyte/cpp
+#include <iostream>
+#include <cmath>
+using namespace std;
+
+void checkOrder(double a, double b) {
+  if (islessequal(a, b))
+    cout << a << " is less than or equal to " << b << endl;
+  else
+    cout << a << " is greater than " << b << endl;
+}
+
+int main() {
+  checkOrder(3.0, 3.0);
+  checkOrder(2.5, 4.1);
+  checkOrder(6.0, 1.0);
+}
+```
+
+## Frequently Asked Questions
+
+### 1. What is the equal function in C++?
+
+C++ does not have a standalone `equal()` function for basic comparisons; equality is typically checked using the `==` operator, or with helper functions like `std::equal()` for ranges.
+
+### 2. What is the math library function in C++?
+
+C++ math functions such as `sqrt()`, `pow()`, `sin()`, and `islessequal()` are provided by the `<cmath>` header.
+
+### 3. Should I use `equals()` or `==` for string compare?
+
+In C++, strings should be compared using `==` when working with `std::string`. The `equals()` method does not exist in standard C++.