isalnum c++

Guri Bee

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19-10-2024

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Demystifying isalnum() in C++: A Guide to Checking Alphanumeric Characters

The C++ isalnum() function is a powerful tool for determining if a given character is alphanumeric. But what exactly does that mean, and how can we use it in our code? Let's dive into the details.

What does "alphanumeric" mean?

Alphanumeric characters encompass both letters (a-z, A-Z) and digits (0-9). The isalnum() function acts as a convenient way to check if a character belongs to this set.

How does isalnum() work?

The isalnum() function is declared in the <cctype> header file. It takes a single character as input and returns a non-zero value if the character is alphanumeric, otherwise, it returns zero.

Example: Understanding isalnum() in Action

Let's see a simple code snippet showcasing isalnum() in action:

#include <iostream>
#include <cctype>

int main() {
  char ch1 = 'a';
  char ch2 = '5';
  char ch3 = '{{content}}#39;;

  if (isalnum(ch1)) {
    std::cout << ch1 << " is alphanumeric" << std::endl;
  } 
  if (isalnum(ch2)) {
    std::cout << ch2 << " is alphanumeric" << std::endl;
  }
  if (isalnum(ch3)) {
    std::cout << ch3 << " is alphanumeric" << std::endl;
  }

  return 0;
}

Output:

a is alphanumeric
5 is alphanumeric

In this example, isalnum() correctly identifies 'a' and '5' as alphanumeric characters, while '