以下程序片段中，语法不正确的是（ ）。
int a, b;
cin >> a + b;
cout << a << "+" << b << '=' << a + b;
int a, b;
cin >> a >> b;
cout << a << "+" << b << '=';
b = b + a;
cout << b << endl;
int a, b;
cin >> a >> b;
int c = a + b;
cout << a << "+" << b << '=' << c;
int a, b;
cin >> a >> b;
cout << a << "+" << b << '=' << a + b;