Linear equation, incompatible types BOOLEAN/LONGINT

Question

I've got exercise about linear equation in Pascal and I've created simple code for comparison input numbers but when I try to run it. I have problem about incompatible types, got BOOLEAN and expected LONGINT.

program LinearEquation;

var
  a, b: real;

begin
  readln(a, b);

  if (b = 0 and a = 0) then
    writeln('INFINITY')
  else if (b = 0 and a <> 0) then
    writeln(1)
  else if (a = 0 and b <> 0) then
    writeln(0)
  else if(b mod a = 0) then
    writeln(1);

  readln;

end.

and

13 / 9 rownan~1.pas
 Error: Incompatible types: got "BOOLEAN" expected "LONGINT"
15 / 14 rownan~1.pas
 Error: Incompatible types: got "BOOLEAN" expected "LONGINT"
17 / 14 rownan~1.pas
 Error: Incompatible types: got "BOOLEAN" expected "LONGINT"
17 / 14 rownan~1.pas
 Error: Incompatible types: got "BOOLEAN" expected "LONGINT"

Answer 1

At least in modern Delphi, and has higher precedence than =, so

a = 0 and b = 0

is interpreted as

(a = (0 and b)) = 0.

But the and operator cannot accept an integer and a floating-point value as operands (two integers would have been OK, though). Hence the error.

Had a and b been integers, 0 and b would have been the bitwise conjunction of 0 and b, that is, 0. Thus, we would have had

(a = 0) = 0.

This reads either true = 0 (if a is equal to 0) or false = 0 (if a is different from 0). But a boolean cannot be compared to an integer, so the compiler would have complained about that.

Still, this was just an academic exercise. Clearly, your intension was

(a = 0) and (b = 0).

Just add the parentheses:

if (b = 0) and (a = 0) then
  writeln('INFINITY')