Написать программу которая рассчитывает значение функции для определенного угла — Pascal(Паскаль)

Program Trig;
  Uses crt;
  Var i,k,q: integer;
      y,z,a: Real;
      cod: String;
  Function tg(z:real):real;
   Begin{tg}
    tg:=sin(z)/cos(z);
   End;{tg}
  Function ctg(z:real):real;
   Begin{ctg}
    ctg:=cos(z)/sin(z);
   End;{ctg}
  Function sec(z:real):real;
   Begin{sec}
    sec:=1/cos(z);
   End;{sec}
     Function cosec(z:real):real;
   Begin{cosec}
    cosec:=1/sin(z);
   End;{cosec}
       Begin{Trig}
         Clrscr;
         Writeln('You are welcomed by the program of a finding of corners.');
         Writeln('The program finds corners for different trigonometrical functions.');
         Writeln('To begin press Enter.');
         Repeat until keypressed;
         Clrscr;
           Writeln('Chose a corner for a value finding:');
         readln(q);
         a:=180/q;
         Repeat
          Writeln('Chose a trigonometrical function:');
          Writeln('1 - sin');
          Writeln('2 - cos');
          Writeln('3 - tg');
          Writeln('4 - ctg');
          Writeln('5 - sec');
          Writeln('6 - cosec');
          Readln(i);
          Case i of
           1: Begin
               y:=sin(Pi/a);
               cod:='sin';
              End;
           2: Begin
               y:=cos(Pi/a);
               cod:='cos';
              End;
           3: Begin
               y:=tg(Pi/a);
               cod:='tg';
              End;
           4: Begin
               y:=ctg(Pi/a);
               cod:='ctg';
              End;
           5: Begin
               y:=sec(Pi/a);
               cod:='sec';
              End;
           6: Begin
               y:=cosec(Pi/a);
               cod:='cosec';
              End;
           Else writeln('Input code of function!!!');
          End;
         Until (i>0) and (i<7);
         Writeln('The value of the ',cod,' functon at an corner = ',y:1:4);
         Repeat until keypressed
       End.{Trig}