Вход в бесконечный цикл при решении уравнения методом простых итераций

#include "stdafx.h"
#include <cmath>
#include <iomanip>
#include <iostream>
using namespace std;
 
double f1(double x1, double x2, double x3,double x4);
double f2(double x1, double x2, double x3,double x4);
double f3(double x1, double x2, double x3,double x4);
double f4(double x1,double x2,double x3,double x4);
 
double g1(double x1, double x2, double x3,double x4);
double g2(double x1, double x2, double x3,double x4);
double g3(double x1, double x2, double x3,double x4);
double g4(double x1, double x2,double x3,double x4);
 
int main()
{
    
    cout<<"\tEnter initial values of params\n";
    double x1;cout<<"x1 = ";cin>>x1;
    double x2;cout<<"x2 = ";cin>>x2;
    double x3;cout<<"x3 = ";cin>>x3;
    double x4;cout<<"x4 =";cin>>x4;
    double er;cout<<"Error of calculations = ";cin>>er;
    for
    (
        double it = 1; 
        er < fabs(f1(x1, x2, x3,x4)) || er < fabs(f2(x1, x2, x3,x4)) || er < fabs(f3(x1, x2, x3,x4))|| er <fabs(f4(x1,x2,x3,x4));
        it = it + 1
    )
    {
        system("cls");
        cout<<"Iteration # "<<setprecision(0)<<it<<endl;
        cout<<"x1 "<<setprecision(0)<<(x1 = g1(x1, x2, x3,x4))<<endl;
        cout<<"x2 "<<setprecision(0)<<(x2 = g2(x1, x2, x3,x4))<<endl;
        cout<<"x3 "<<setprecision(0)<<(x3 = g3(x1, x2, x3,x4))<<endl;
         cout<<"x4 "<<setprecision(0)<<(x4 = g4(x1, x2, x3,x4))<<endl;
    }
    cout<<"f1(x1, x2, x3) = 0.77*x1+0.44*x2+0.21*x3+0.18*x4+1.24 = "<<f1(x1, x2, x3,x4)<<endl;
    cout<<"f2(x1, x2, x3) =  0.45*x1+1.23*x2+0.06*x3+0.00*x4-0.88 = "<<f2(x1, x2, x3,x4)<<endl;
    cout<<"f3(x1, x2, x3) = 0.26*x1+0.34*x2+(-1.11)*x3+0.00*x4+0.62     = "<<f3(x1, x2, x3,x4)<<endl;
    cout<<"f4(x1,x2,x3,x4)=0.05*x1+(-0.26)*x2+0.34*x3+(-1.12)*x4-1.17 ="<<f4(x1,x2,x3,x4)<<endl;
    system("pause");
    return 0;
}
 
double f1(double x1, double x2, double x3,double x4)
{
    return 0.77*x1+0.44*x2+0.21*x3+0.18*x4+1.24;
}
 
double f2(double x1, double x2, double x3,double x4)
{
    return 0.45*x1+1.23*x2+0.06*x3+0.00*x4-0.88;
}
 
double f3(double x1, double x2, double x3,double x4)
{
 
    return 0.26*x1+0.34*x2+(-1.11)*x3+0.00*x4+0.62;
}
 
double f4(double x1, double x2, double x3,double x4)
{
    return 0.05*x1+(-0.26)*x2+0.34*x3+(-1.12)*x4-1.17;
 
}
double g1(double x1, double x2, double x3,double x4)
{
    return x1 - 0.01*f1(x1, x2, x3,x4);
}
 
double g2(double x1, double x2, double x3,double x4)
{
    return x2 - 0.01*f2(x1, x2, x3,x4);
}
 
double g3(double x1, double x2, double x3,double x4)
{
    return x3 - 0.01*f3(x1, x2, x3,x4);
}
double g4(double x1, double x2, double x3,double x4)
{
    return x4 - 0.01*f4(x1, x2, x3,x4);
}