so i have this project for school to create a pascal program. i was thinking of making a calculator which can do stuff like cosine and all that stuff. like a scientific calculator. The program has to use crt because thats all weve learnt so far. im not an expert at pascal but i still understand some stuff like loops and menus and such. would the only way to make this be a menu saying stuff like 1) Plus, 2) Minus and so on? or is it possible to just enter in a whole line like 1+4 and then you get the answer? all i want is the basic layout of the program to start off with and then i can build it up.

This is a simple calculator ( addition supported only ):

function calculate(s:string):string;
 var sl:byte absolute s; {lenght of s}
     a1,a2:real;
     i:byte;
 function to_val(si:string):real;
  var r:real;
      c:integer;
  begin
   val(si,r,c);
   to_val:=r;
  end;
 begin
  if sl>2 then begin  {must at least 3 char long }
   i:=pos('+',s);     {only addition is supported}
   if i=0 then s:='Syntax error' else begin
    a1:=to_val(copy(s,1,i-1));
    a2:=to_val(copy(s,i+1,sl-i));
    str(a1+a2:6:4,s);
   end;
  end;
  calculate:=s;
 end;


begin
 writeln(calculate('145+345'));
end.