isalnum() function in C Language
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
#include <ctype.h>
#include <stdio.h>
int main()
{
char ch = 'a' ;
if ( isalnum (ch))
printf ("\nEntered character is alphanumeric\n");
else
printf ("\nEntered character is not alphanumeric\n");
}
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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 <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;
}
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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
#include <ctype.h>
#include <stdio.h>
int ttl_alphanumeric( int i, int counter)
{
char ch;
char a[50] = "www.geeksforgeeks.org";
ch = a[0];
while (ch != '\0' ) {
ch = a[i];
if ( isalnum (ch))
counter++;
i++;
}
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;
}
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Output:
Number of alphanumerics in the given input is : 19
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