Variable still uninitialized after prior assignment in the same cout statement

Question

I am new to programming and was doing a practice with expressions on Visual Studio 2015. I first built this program:

#include <iostream>

int main(void)
{
    int x;

    std::cout
        << "The expression x = 100 has the value " << (x = 100) << ".\n"
        << "Now x has the value " << x << ".\n"
        << "The expression x < 3 has the value " << (x < 3) << ".\n"
        << "The expression x > 3 has the value " << (x > 3) << ".\n";

    system("pause");
    return 0;
}

And the compiler gave an error warning: uninitialized local variable 'x' used in line 11. It's the line << "The expression x > 3 has the value " << (x > 3) << ".\n";. I changed the program to:

    ...
    std::cout
        << "The expression x = 100 has the value " << (x = 100) << ".\n";
    std::cout
        << "Now x has the value " << x << ".\n"
        << "The expression x < 3 has the value " << (x < 3) << ".\n"
        << "The expression x > 3 has the value " << (x > 3) << ".\n";
    ...

And the warning disappeared. My question is, in the first program, why is x still uninitialized after I have assigned 100 to it? Why is the error in line 11 but not in line 9 or 10? Is there a way to fix the problem without splitting the cout statement?