What is the relevance of if (!(cin >> variableName)) in this loop

I'm a self taught developer trying to learn c++, I found this exercise on google and I wrote the code for it, though all my conditions were correct, it wouldn't work, when I checked their answer, I found this line of code- if (!(cin >> guess)). I honestly don't see the relevance, I don't know why it made my loop not to work. Here is my code:

int main(int argc, char* argv[])    
{

int nUserRandNum = 0;
    int randomNumber=0;

    srand (time(NULL));
    randomNumber = rand() % 100 + 1;

    printf("Please enter a random number between 1 - 99 \n");

    scanf("%d", &nUserRandNum);


    do
    {
        if (randomNumber < nUserRandNum)
        {
            printf("Try to go a little higher than \n", nUserRandNum);
        }
        else
        {
            printf("You might want to go a little lower than \n", nUserRandNum);    
        }
    }
    while (randomNumber != nUserRandNum);

    printf("You got it!!!");

    system("Pause"); 

    return 0;
}

When I checked the answer they had:

int random_number, guess;

// Initialize random seed.
srand (time(NULL));

// Generate random number between 1 and 100
random_number = rand() % 100 + 1;

cout << "Guess our number (1 to 100) ";
cin>>guess;
do 
{
    if (!(cin >> guess)) 
    {
      cout << "Please enter only numbers" << endl;
    } 
    else 
    {
      if (random_number < guess) 
          cout << "The secret number is lower than " << guess << endl;
      else if (random_number > guess) 
          cout << "The secret number is higher than " << guess << endl;
    }
} while (random_number != guess);
cout << "Congratulations!" <<  endl;

what does that if statement do {if (!(cin >> guess)) }? And are there other reasons my loop didn't work?