Error C2106: '=' : left operand must be l-value С++

#include <iostream.h>
#include <stdio.h>
#include <math.h>
int main() {
double Xn, Xk, dX, a, b, c, F;
printf("Enter Xn, Xk, dX, a, b, c \n");
scanf("%lf%lf%lf%lf%lf%lf", &Xn, &Xk, &dX, &a, &b, &c);
printf(" -----------------------\n");
printf("| X | F |\n");
printf(" -----------------------\n");
double x = Xn;
while (x <= Xk){
if (x = 0 && b != 0) F = a * pow(x + c,2) - b;
if (x = 0 && b = 0) F = ((x - a)/(-c));
else F = (a + (x / c));
x += dX;
}
printf("---------------------\n");
return 0;
}

Ошибку выдаёт на if (x = 0 && b = 0) F = ((x - a)/(-c));
в чём проблема?