# isinf() function in C++

• Last Updated : 27 Sep, 2018

This function is defined in <cmath.h> .The isinf() function is use to determine whether the given number is infinity or not i.e positive infinity or negative infinity both. This function returns 1 if the given number is infinite otherwise this function returns zero.

Syntax:

Want to learn from the best curated videos and practice problems, check out the C++ Foundation Course for Basic to Advanced C++ and C++ STL Course for foundation plus STL.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.
`bool isinf( float arg );`

or

`bool isinf( double arg );`

or

`bool isinf( long double arg );`

Parameter: This function takes a mandatory parameter x which represents the given floating point value.

Return: This function returns 1 if the given number is infinite else return zero.

Below programs illustrate the isinf() function in C++:

Example 1:- To show infinite case which returns 1

 `// c++ program to demonstrate``// example of isnormal() function.`` ` `#include `` ` `using` `namespace` `std;`` ` `int` `main()``{`` ` `    ``float` `f = 6.0F;`` ` `    ``// check for +ve infinite value``    ``cout << ``"isinf(6.0/0.0) is = "` `<< isinf(f/0.0) << endl;`` ` `    ``// check for -ve infinite value``    ``f = -1.2F;``    ``cout << ``"isinf(-1.2/0.0) is = "` `<< isinf(f/0.0) << endl;`` ` `    ``return` `0;``}`
Output:
```isinf(6.0/0.0) is = 1
isinf(-1.2/0.0) is = 1
```

Explanation: In example 1 the floating point number represents infinity that’s why function returns 1.

Example 2:- To show non-infinite case which returns 0

 `// c++ program to demonstrate``// example of isinf() function.`` ` `#include ``using` `namespace` `std;`` ` `int` `main()``{``   ``cout << ``"isinf(0.0) is = "` `<< isinf(0.0) << endl;`` ` `   ``cout << ``"isinf(sqrt(-1.0)) is = "` `<< isinf(``sqrt``(-1.0)) << endl;`` ` `   ``return` `0;``}`
Output:
```isinf(0.0) is = 0
isinf(sqrt(-1.0)) is = 0
```

Exception: In example 2 the given floating point number is not representing infinity that’s why function returns zero.

My Personal Notes arrow_drop_up