Найти значение y(x) по формуле линейной интерполяции - Turbo Pascal

uses crt;
const n=4;
      x:array[1..n] of real=(1,1.1,2,2.2);
      y:array[1..n] of real=(0,0.1,0.2,0.3);
var x1,y1:real;
    i,i1:byte;
begin
clrscr;
x1:=1.18;
i:=0;
while(i<n)and(i1=0) do
if x[i]>=x1 then i1:=i
else inc(i);
y1:=y[i-1]+(x1-x[i1-1])/(x[i]-x[i1-1])*(y[i]-y[i-1]);
write('При х=1.18 y=',y1:0:4);
readln
end.