How to check if number of inputs required is correct or not

I am having a simple problem I cannot figure out by myself for some reason. I am trying to have the user input 4 different numbers at one time. Now the problem I am having is I want to check if they have inputted 4 numbers or not. So if the user only inputs 3 numbers (say 1,2,3) I want to output an error message and return them back to inputting 4 numbers. Same if they input say 5 numbers (say 1,2,3,4,5), output error message and return to input screen.

I have an idea as to how to do this but not too sure anymore. I think it would be something along the lines of:

void askUser()
{
   int nums;
   cin >> nums;
   while (int i = 4)            // have a for loop here to check if it 
   {                            // has 4 numbers inputted
      for (?)                   // this is where I am having a problem
      {
         //output numbers or output error message
         cout << nums << endl;

         else 
          cout << "Wrong amount of input! Please input 4 values" << endl;
          return *back to input screen*
      }
  }

I saw another question on stack overflow that is a bit similar to this except that in the other question they are dealing with words and I am not to sure how to go about it without trying what they were doing. The other question I saw that is closest to this titled "C++ check for specific number of input". Thank you and hopefully this is asked properly.