Why I have comperror? Deleting <math.h> gives nothing.

#include <iostream.h>
#include <math.h>
//#include <fstream.h>
const int MaxN = 1000001;
//const double koef== 0.70710678119;
int main()
{//ifstream in("c:/input.txt", ios::in);
double koef;
koef=sqrt(2.0);
koef/=2;
char a[MaxN]="";
//cin.getline(a, MaxN);
int i=0;
while (cin.get(a[i]));
double x=0.,y=0.;
char* pa=a;
while (*pa && *pa!='0')
  {if (*pa=='9') {x+=koef;y+=koef;}
  if (*pa=='8') {x-=koef;y+=koef;}
  if (*pa=='7') {x++;y++;}
  if (*pa=='6') {x++;}
  if (*pa=='4') {x--;}
  if (*pa=='3') {x+=koef;y-=koef;}
  if (*pa=='2') {x--;y--;}
  if (*pa=='1') {x-=koef;y-=koef;}
  pa++;
  }
//cout.precision(10);
//cout<<fixed<<x<<" "<<y;
printf("%.10lf",x);
cout<<" ";
printf("%.10lf",y);
return 0;
}

Change
#include <iostream.h>
to
#include <iostream>
using namespace std;

or add
#include <stdio.h>

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