found this as a guide on the web, does it run for anyone?

Hi,

I'm too new to tell what's going wrong. Anyone have a minute or two?

void setup () {
   Serial.begin (9600);
   Serial.print ("According to isdigit:\r");
   Serial.print (isdigit( '8' ) ? "8 is a": "8 is not a");
   Serial.print (" digit\r" );
   Serial.print (isdigit( '8' ) ?"# is a": "# is not a") ;
   Serial.print (" digit\r");
   Serial.print ("\rAccording to isalpha:\r" );
   Serial.print (isalpha('A' ) ?"A is a": "A is not a");
   Serial.print (" letter\r");
   Serial.print (isalpha('A' ) ?"b is a": "b is not a");
   Serial.print (" letter\r");
   Serial.print (isalpha('A') ?"& is a": "& is not a");
   Serial.print (" letter\r");
   Serial.print (isalpha( 'A' ) ?"4 is a":"4 is not a");
   Serial.print (" letter\r");
   Serial.print ("\rAccording to isalnum:\r");
   Serial.print (isalnum( 'A' ) ?"A is a" : "A is not a" );


   
}

void loop () {

}

It will never compile because you are missing a section of the code. What you have is a snippet of some code

It will never compile because you are missing a section of the code. What you have is a snippet of some code

Odd because it compiles and runs fine apart from the lack of newlines.

Lose the \r's and use println for newlines. Or change the \r to \n which is a newline character.

And there’s a load of apparent typos in the characters being compared against what they output....
Second isdigit is still comparing ‘8’ instead of ‘#’
Last 3 isalpha are comparing ‘A’ instead of ‘b’, ‘&’ and ‘4’
isalnum example seem to stop dead, so does indeed seem to be missing code.

Unless the OP retyped this, doesn’t seem the greatest example.

Thanks, folks.