Какой знак используется при вычислении остатка от деления​

//g++ -Wall -o 1 1.cpp

//./1

#include <iostream>

#include <algorithm>

#include <vector>

using namespace std;

int main() {

   int n;

   cin>>n;

   if (n == 0){

       cout<<0;

       return 0;

   }

   else{

       int a1 = 0 , a2 = 1;

       int c = 1;

       while(a2<=n){

           if (a2==n){

               cout<<c;

               return 0;

           }

           a1 = a2;

           a2 = a1+a2;

           c++;

       }

       cout<<-1;

       return 0;

   }

}

Объяснение:

Магический квадрат с n сторон

const
  mn = 16;
var
  p: Boolean;
procedure Swap(var a, b: Integer);
var
T: Integer;
begin
T := a; a := b; b := T
end;
procedure CreateMagic(n: Integer);
var
i, j, k, s, b, r, m: Integer;
a: Array[1.. mn, 1.. mn] Of Integer;
begin
  p := True; 
if Odd(n) Then
begin
i := 1; j := Succ(n div 2);
for k := 1 To Sqr(n) do
begin
a[i, j] := k;
if k mod n = 0 Then Inc(i)
Else
begin
Dec(i); Inc(j);
if i = 0 Then i := n;
if j > n Then j := 1
end
end;
  end
Else
if n mod 4 = 0 Then
begin
k := 1;
for i := 1 To n Do
for j := 1 To n Do
begin
a[i, j] := k; Inc(k)
end;
j := 2; m := n div 2;
for i := 1 To m Do
for k := 1 To m Div 2 Do
begin
if j = Succ(m) Then j := 2
Else
if j = (m + 2) Then j := 1;
s := Succ(n - i); b := Succ(n - j);
Swap(a[i, j], a[s, b]);
Swap(a[i, b], a[s, j]);
Inc(j, 2)
end
  end
Else
if n <> 2 Then
begin
k := 1;
for i := 1 To n Do
for j := 1 To n Do
begin
a[i, j] := k; Inc(k)
end;
  r := Pred(n div 2) div 2; m := n div 2;
for i := 1 To m Do
begin
j := i;
for k := 1 To r Do
begin
if j > m Then j := 1;
s := Succ(n - i); b := Succ(n - j);
Swap(a[i, j], a[s, b]);
Swap(a[i, b], a[s, j]);
Inc(j)
end
  end;
i := 1;
for k := 1 To m Do
begin
if j > m Then j := 1;
s := Succ(n - i);
Swap(a[i, j], a[s, j]);
Inc(i); Inc(j)
  end;
i := 1; j := r + 2;
for k := 1 To m Do
begin
if j > m Then j := 1;
b := Succ(n - j);
Swap(a[i, j], a[i, b]);
Inc(i); Inc(j)
end
  end
  Else p := False;
if p Then
begin
for i := 1 To n Do
begin
for j := 1 To n Do
Write(a[i, j]: 4);
WriteLn
end
end
Else
WriteLn( 'do not exists' )
end;
var
  n: Integer;
begin
WriteLn('n = '); ReadLn(n);
  CreateMagic(n);
end.