isalnum() function in C Language

isalnum() function in C programming language checks whether the given character is alphanumeric or not. isalnum() function defined in ctype.h header file. Alphanumeric: A character that is either a letter or a number. Syntax:

int isalnum(int x);

Examples:

Input : 1
Output : Entered character is alphanumeric
Input : A
Output : Entered character is alphanumeric
Input : &
Output : Entered character is not alphanumeric

Output:

Entered character is alphanumeric

isalnum() function returns some value. It always returns '8' for all characters except special characters like (#,@,% etc.). It will always return '0' for special characters.

Input: 'A'                                                                                                                                                                                                                

Output: 8

Input: 'b'

Output:8

Input: '4'

Output: 8

Input: '#'

Output: 0

Input: '?'

Output: 0

Application: isalnum() function is used to find out number of alphanumeric in a given sentence(or any input). Example:

Input: abc123@
Output: Number of alphanumerics in the given input is : 6
Input: a@#
Output: Number of alphanumerics in the given input is : 1
Input: ...akl567
Output: Number of alphanumerics in the given input is : 6

Output:

Number of alphanumerics in the given input is : 19