ROT13: proc options(main);                            
Rot13: proc (c) returns (char (1));                   
  dcl c char (1);                                     
  dcl low char(26) init ('abcdefghijklmABCDEFGHIJKLM');
  dcl hig char(26) init ('nopqrstuvwxyzNOPQRSTUVWXYZ');
  dcl i bin fixed (15);                               
  i = index (low, c);                                 
  if (i ^= 0) then                                    
    return (substr(hig,i,1));                         
  i = index (hig,c);                                  
  if (i ^= 0) then                                    
    return (substr(low,i,1));                         
  return (c);                                         
end Rot13;                                            
dcl c char(1);                                        
dcl eof bit(1) init ('0'b);                           
on endfile(sysin) begin;                              
  eof='1'b;                                           
end;                                                  
do while (^eof);                                      
  get edit (c) (a(1));                                
  put edit (Rot13(c)) (a(1)); 
end;                          
end ROT13;