i cannot under stand this error in c++

Question

error: no match for 'operator=' (operand types are 'std::basic_ostream<char>' and 'int')|
this is what is wrote =>
{
cout << " The INFINITE 4X MULTIPLIER\n\n\n\n\n\n\n";
int a;
int b;
int c;
int d;
int sum1;
//sum1 = a*b*c*d;
int sum2;
//sum2 = a*b*c;

cout<<"HOW TO USE IT:-\n\n";
cout<<"1.blablabla<<endl;
cin>>a;
cin>>b;
cin>>c;
cin>>d;
if(sum1=0){cout<<"product is =\n"<<sum2=a*b*c;}
else{cout<<sum1=a*b*c*d;}
}

according to compiler error is in last line

Answer 1

You forgot a double quote in cout<<"1.blablabla<<endl;

Answer 2

in if you can't cout<<"product is =\n"<<sum2=a*b*c;
because you can't assign value in cout ;)
also not in else