listen carefully :D
program p;
(*the main program's global section*)
uses crt;
var a,b:integer;
c:real;
(*p2 forward,so can be call from anywhere*)
procedure p2(x:integer; var y:integer); forward;
(*p1 declaration---------------------*)
procedure p1 (x:integer; var y:integer);
(*here is the local section of p1
these variables are lives inside p1
and wiped out when p1 ends its running*)
var c:integer;
pt:^integer; {pointer declaration}
begin { (1) } (*p1's body*)
writeln(a,b,x,y);
new (pt);
if (x<2) and (y<2) then
if x>y then begin
y:=x;
writeln(a,b,x,y);
p2(x,b);
end;
dispose(pt);
end;
(*end of p1--------------------------*)
(*main declaration of p2-------------*)
procedure p2 (x:integer; var y:integer);
begin { (2) }
writeln(a,b,x,y);
c:=a;
if (a<2) and (b<2) then
if x=y then begin
x:=y+1;
writeln(a,b,x,y);
p1(a,y);
end;
end;
(*end of p2-------------------------*)
(*here begins the main program*)
begin { (3) }
clrscr;
(*initialize the global vars*)
a:=1;
b:=0;
c:=0.0;
(*call p1 with a,and b parameters.*)
p1(a,b);(*a=1,b=0*)
(*the main program remember the position of calling
and jump up to the p1 procedure to take action*)
(*
First call of p1 with these parameters
a=1,b=0
p1(a,b);
so after that
p1 creates its vars
var c:integer;
pt:^integer;(it is contains a memoria address,that stores an integer value)
when the program reaches the p1's begin section then
p1 writes out the variables' data to the screen.
writeln(a,b,x,y); {like 1010}
then,we reserves a memoria place manually for our pointer
new (pt);
then p1 is analyzes the results as
if (x<2) and (y<2) then {if it is true,of course true 'cause x=1,and y=0}
the following commands are running
if x>y then begin {it is true too,'cause x=1 and y=0}
y:=x; {y's value changes to x's value,so y=1,till y is lives,the end of p1 running}
writeln(a,b,x,y);{these results appears on the screen: 1111}
then p1 is calling p2 to take action with its parameters.
p1 remembers this position in its body and jump to p2.
{x=1 and b=1}
p2(x,b); {p2 running...}
p2 writes these results to the screen
writeln(a,b,x,y); {1111}
and then p2 adds a new value to the global variable c
c:=a; {so c=1.0}
and p2 is checking ...
if (a<2) and (b<2) then {a=1 ,b=1 so a<2=true,b<2=true,...true and true = true}
{so the following commands are running...}
if x=y then begin {it is true ,so then}
x:=y+1; {x's value changes to y+1=2,so x=2}
writeln(a,b,x,y);{the results are: 1121}
{p2 remembers its body's position and calls p1}
p1(a,y);{'cause the if statement result is true,p2 calls p1}
{a=1,y=1}
p1(a,y); is running...
p1 creates its vars
var c:integer;
pt:^integer;
when the program reaches the p1's begin section then
p1 writes out the variables' data to the screen.
writeln(a,b,x,y); {like 1111}
then,we reserves a memoria place manually for our pointer
new (pt);
then p1 is analyzes the results
if (x<2) and (y<2) then {it is true so commands follows..}
if x>y then begin {but it is false}
y:=x;
writeln(a,b,x,y);
p2(x,b);
end;
so p1 is wipe out the reserved area....
dispose(pt);
and then end follows,so jump back to p2
and p2 is ends too,so jump back to p1
end;
p1 is back,and continues its work
dispose(pt);{wipes out reserved area.. }
and when p1 is ends its running the controlling is back to the caller main
program
end;
*)
{the main program writes the results to the screen}
writeln(a,b);{11}
end.
(*and this is the end of the main program.*)
(*Created by FlamingClaw 2010.03.28.Hungary*)
