include ctype.h library

Hello

where can I download ctype.h library and what is the location in ArduinoIDE IDE, I am using latest version of IDE.

objective is to use isAlpha() function and isDigit() function in programming.

--
Thanks in Advance

It's part of the ide install. No need to download just
#include <ctype.h>

Use the correct name (case matters)...

void setup() 
{
  Serial.begin( 115200 );
}

void loop() 
{
  if (Serial.available() > 0) 
  {
    if( isalpha( Serial.read() ) );
    {
      Serial.println( F( "isalpha" ) );
    }
  }
}

I am not able to see in the installed library folder.

Objective is I need to check the user has entered only digit, otherwise the program should throw error message to the user to repeat the loop until correct input is achieved.

--
Thanks in advance

just do it. Report if there is an error. It's not in the 'library' folder. If you do a simple search, you'll find it.