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
// C code to illustrate isalphanum() #include <ctype.h> #include <stdio.h> int main()
{ char ch = 'a' ;
// checking is it alphanumeric or not?
if ( isalnum (ch))
printf ("\nEntered character is alphanumeric\n");
else
printf ("\nEntered character is not alphanumeric\n");
} |
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
#include <iostream> #include <cctype> // header file for function isalnum() using namespace std;
int main() {
char ch;
cin>>ch;
cout << " function will return: " << isalnum (ch);
return 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
// C code to illustrate isalphanum() #include <ctype.h> #include <stdio.h> int ttl_alphanumeric( int i, int counter)
{ char ch;
char a[50] = "www.geeksforgeeks.org";
ch = a[0];
// counting of alphanumerics
while (ch != '\0' ) {
ch = a[i];
if ( isalnum (ch))
counter++;
i++;
}
// returning total number of alphanumerics
// present in given input
return (counter);
} int main()
{ int i = 0;
int counter = 0;
counter = ttl_alphanumeric(i, counter);
printf ("\nNumber of alphanumerics in the "
"given input is : %d", counter);
return 0;
} |
Output:
Number of alphanumerics in the given input is : 19