int iscntrl(int chr);

Tests if a character a control character

#include <stdio.h> /* including standard library */
//#include <windows.h> /* uncomment this for Windows */
 
#include <ctype.h>
 
int main ( void )
{
  int i;
  char string[11]="Test\n-!&%1";
  for (i=0; i <= 11;i++)
    {
     if ( iscntrl(string[i]) != 0 )
      {
       printf("Character %i is a control char\n",i);
      }
    }
  return 0;
}

  user@host:~$ ./iscntrl 
  Character 4 is a control char
  Character 10 is a control char
  Character 11 is a control char