Где ошибка ?

#include<iostream.h>
#include<math.h>
#include<conio.h>
void main ()
{ clrscr();
int i,n;
double s,a,x;
cout<<"Vvedite n and x"<<endl;
cin>>n;
cin>>x;
a=x;
s=0;
for (i=1;i<=n;i++)
{
a=sin(a);
s+=a;
}
cout<<s<<endl;
getch();
}

a=sin(a);

for (j=1;j<=i;j++)
{
a=sin(a);
}

#include<iostream.h>
#include<math.h>
#include<conio.h>
void main ()
{ clrscr();
int i,n;
double s,a,x;
cout<<"Vvedite n and x"<<endl;
cin>>n;
cin>>x;
a=x;
s=0;
for (i=1;i<=n;i++)
{
   {a=sin(a);}
s+=a;
}
cout<<s<<endl;
getch();
}

#include<iostream.h>
#include<math.h>
#include<conio.h>
void main ()
{ clrscr();
int i,j,n;
double s,a,x;
cout<<"Vvedite n and x"<<endl;
cin>>n;
cin>>x;
a=x;
s=0;
for (i=1;i<=n;i++)
{
for (j=1;j<=i;j++) a=sin(a);
s+=a;
}
cout<<s<<endl;
getch();
}

sin(a * M_PI / 180)

#include <cstdlib>
#include <iostream>
#include <math.h>
using namespace std;
 
int main(int argc, char** argv) {
    float a, b;
    a = sin(3.14);
    b = sin(180);
    cout << "a = " << a << endl;
    cout << "b = " << b << endl;
    return 0;
}

#include <iostream>
#include <cmath>
 
int main()
{
    std::cout << sin(30);
    return 0;
}

#include <iostream>
#include <cmath>
 
int main()
{
    std::cout << sin(30 * M_PI / 180);
    return 0;
}

sin(a * M_PI / 180)