А что значит clrscr; ?))

if x[i]=y[i] then k:=k+1;

program integral;
var
n,i : integer;
a,b,shag,sum,itog : real;

function F(x:real):real;
begin
  F:=sin(2*x);
end;

begin
write('na4alo integrirovaniya a = '); readln(a);
write('konec integrirovaniya b = '); readln(b);
write('koli4estvo razbieniy intervala n = '); readln(n);

shag:=(b-a)/n;
sum:=0;
for i:=1 to n-1 do
  sum := sum + F(shag*i+a);
sum := sum + (F(a)+F(b))/2;

itog:=(b-a)/n * sum;
writeln('integral = ', itog:0:5);
readln;
end.