isalnum in C Programming

The C isalnum() function is one of the Standard Library Function available in C language, which is used to check the given character is either an alphabet or a numeric value.

In this article we will show you, How to use isalnum in C Programming language with example. Before we get into the example, the basic syntax of the isalnum in C language is as shown below.

C isalnum Function syntax

Below c isalnum function will accept the single character as the parameter, and check whether the given character is either a number, or an alphabet.

isalnum(char)

isalnum in C Programming Example

The isalnum method (alpha numeric) is used to find the given character is either an alphabet, or numeric. This C program allows the user to enter any character, and check whether the character is between A to Z, or a to z, or a numeric value using the isalnum function.

//Example for isalnum in C Programming
#include <stdio.h>
#include <ctype.h>

int main()
{
    char ch;
    printf("Please Enter Either an Alphabet, or a Number: \n");
    scanf("%c", &ch);

    if(isalnum(ch))
    {
      printf("\n You have entered an Alphanumeric Character");         
    }
    else
    {
      printf("\n %c is not an Alphanumeric Character", ch);
      printf("\n I request you to enter Valid Number, or an Alphabet");	
    }
}

OUTPUT

Let me enter the Uppercase letter

Let me enter the Numeric value

ANALYSIS

In this isalnum in c program, first we declared a character variable called ch. Following statement will ask the user to enter any character. And then we are using the scanf to assign the user entered character to ch variable

printf("Please Enter Either an Alphabet, or a Number: \n");
scanf("%c", &ch);

In this next line, we added the If Statement to check whether the character is between ‘A’ to ‘Z’, or ‘a’ to ‘z’, or a number using isalnum function. If the condition is True then the following statement will be printed

printf("\n You have entered an Alphanumeric Character");

If the above condition is FALSE then the given character is not an Alphabet, or a number. So, it will print below statements

printf("\n %c is not an Alphanumeric Character", ch);
printf("\n I request you to enter Valid Number, or an Alphabet");

Above c isalnum code is perfectly checking whether the given character is either an alphabet or a number. But what if, we enter the symbols

Let me try with the space character

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