# isless() in C/C++

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)
```

Parameters:

• a, b => These two are the parameters whose value we want to compare.
• Result:

• The function will return the true if a<b else it returns false.
• Error:

• No error occurs with this function.
• Exception:

• If a or b or both is NaN, then the function raised an exception and return false(0).

 `// 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 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 vaiable 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 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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