PASCAL procedure won't read value from an external variable

Question

Given a, b and c, calculate: 2^a + 2^b + 2^c.

program power;
var a,b,c, r1,r2,r3 :integer;
    
procedure power2(pwr :integer; var result :integer);
var i :integer;
    
begin
    
i := 1;
result := 1;
    
while pwr <= i do
    begin

    result := result * 2;
    i := i + 1;
        
    end;
    
end;
   
   
begin {main}

write('a: ');
readln(a);
write('b: ');
readln(b);
write('c: ');
readln(c);

power2(a, r1);
power2(b, r2);
power2(c, r3);

writeln('power: ', r1 + r2 + r3);
  
end.

Why does the program fail to do the while loop?

The program prints 3 instead of the sum of r1, r2, r3, independently of the input (a,b,c). How do I fix this?

Answer 1

You are incorrect about the while loop comparison, pwr <= i. It should be the other way around.

procedure power2(pwr :integer; var result :integer);
var i :integer;
begin    
  i := 1;
  result := 1;    
  while i <= pwr do
    begin    
      result := result * 2;
      i := i + 1;        
    end;    
end;