isalnum() - ctype.h

The C library function void isalnum(int c) checks if the passed character is alphanumeric.
This function returns non-zero value if c is a digit or a letter, else it returns 0.

Syntax

int isalnum(int c);

Example

#include <stdio.h>
#include <ctype.h>

int main()
{
   int var1 = 'd';
   int var2 = '2';
   int var3 = '\t';
   int var4 = ' ';
    
   if( isalnum(var1) )
   {
      printf("var1 = |%c| is alphanumeric\n", var1 );
   }
   else
   {
      printf("var1 = |%c| is not alphanumeric\n", var1 );
   }
   
   if( isalnum(var2) )
   {
      printf("var2 = |%c| is alphanumeric\n", var2 );
   }
   else
   {
      printf("var2 = |%c| is not alphanumeric\n", var2 );
   }
   
   if( isalnum(var3) )
   {
      printf("var3 = |%c| is alphanumeric\n", var3 );
   }
   else
   {
      printf("var3 = |%c| is not alphanumeric\n", var3 );
   }
   
   if( isalnum(var4) )
   {
      printf("var4 = |%c| is alphanumeric\n", var4 );
   }
   else
   {
      printf("var4 = |%c| is not alphanumeric\n", var4 );
   }
   return(0);
}

Output / Return Value

var1 = |d| is alphanumeric
var2 = |2| is alphanumeric
var3 = |        | is not alphanumeric
var4 = | | is not alphanumeric

Limitations

Alternatives / See Also

Reference