isalnum() function in C Language (original) (raw)

Last Updated : 26 Dec, 2022

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 `

// 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

C++ `

#include #include // 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 `

// 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