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# isless() in C/C++

• Last Updated : 20 Feb, 2023

In C++, isless() is a predefined function used for mathematical calculations. math.h is the header file required for various mathematical functions.
isless() function used to check whether the 1st argument given to the function is less than the 2nd argument given to the function or not. Means if a is the 1st argument and b is the 2nd argument then it check whether a<b or not.
Syntax:

`bool isless(a, b)`

Time Complexity: O(1)

Auxiliary Space: O(1)

## CPP

 `// CPP code to illustrate``// the exception of function``#include ``using` `namespace` `std;` `int` `main()``{``    ``// Take any values``    ``int` `a = 5;``    ``double` `b = nan(``"1"``);``    ``bool` `result;` `    ``// Since b value is NaN so``    ``// with any value of a, the function``    ``// always return false(0)``    ``result = isless(a, b);``    ``cout << a << ``" isless than "` `<< b``         ``<< ``": "` `<< result;` `    ``return` `0;``}`

Output:

`5 isless than nan: 0`

Example:

• Program:

## CPP

 `// CPP code to illustrate``// the use of isless function``#include ``using` `namespace` `std;` `int` `main()``{``    ``// Take two any values``    ``int` `a, b;``    ``bool` `result;``    ``a = 5;``    ``b = 8;` `    ``// Since 'a' is not greater``    ``// than 'b' so answer``    ``// is true(1)``    ``result = isless(a, b);``    ``cout << a << ``" isless than "` `<< b``         ``<< ``": "` `<< result << endl;` `    ``char` `x = ``'a'``;` `    ``// Since 'a' ascii value is less``    ``// than b variable so answer``    ``// is true(1)``    ``result = isless(x, b);``    ``cout << x << ``" isless than "` `<< b``         ``<< ``": "` `<< result;` `    ``return` `0;``}`

Output:

```5 isless than 8: 1
a isless than 8: 0```

Note: Using this function you can compare any data type with any other data type as well.
Application
There are variety of applications where we can use isless() function to compare two values like to use in while loop to print the first 9 natural number.

## CPP

 `// CPP code to illustrate``// the use of isless function``#include ``using` `namespace` `std;` `int` `main()``{``    ``int` `i = 1;``    ``while` `(isless(i, 10)) {``        ``cout << i << ``" "``;``        ``i++;``    ``}``    ``return` `0;``}`

Output:

`1 2 3 4 5 6 7 8 9 `

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