In #key# C++: Object-Oriented Programming Language #key#, **`isalnum()`** is used to check if the input value is either an alphabet or a number. 

# 
## Syntax

```c++
int isalnum(char ch);
```

## Parameters
`ch`: a character of type `char`.

> `char` in C++ is a special type of datatype that deals with alphabet values. From a memory perspective, C++ `char` is of 1 byte.

# 
## Return value
* `Nonzero`: if the argument values are in the range (`a-z`,`A-Z`,`0-9`), then `isalnum` returns a non-zero value, i.e., `TRUE`.

* `0`: if the argument is not between the defined range(`a-z`,`A-Z`,`0-9`), then `isalnum` returns 0, i.e., `FALSE`.


## Code
In the example below, we pass the English alphabet `a` as an argument, which returns a non-zero value.

#include <iostream>
using namespace std;

int main() {
  int num = isalnum('a');
  if (num) {
    cout << "TRUE at " << num;
  } else
    cout << "FALSE at " << num;
  return 0;
}

What is isalnum() in C++?

isalnum() checks if a char is an alphabet or number, returning nonzero for true, 0 for false.