7.6 from C++ Primer - c++

Question

int main()
{
cout << "The maximum number of elements in an array is 100. " << endl;
const int MAX = 100;
double myarray[MAX];
int arraysize = Fill_Array(myarray, MAX);
Show_Array(myarray, arraysize);
Reverse_Array(myarray, arraysize);
Show_Array(myarray, arraysize);
Reverse_Positions(myarray, arraysize);
Show_Array(myarray, arraysize);
return 0;
}
int Fill_Array(double ar[], int size)
{
int i = 0;
cout << "\nEnter a double value (Enter q to quit): ";
while (cin >> ar[i] && i < size)
{
i++;
cout << "Enter next value: ";
}
return i;
}
void Show_Array(const double ar[], int size)
{
cout << "\nHere is your array: " << endl << endl;
for (int i = 0; i < size; ++i)
cout <<"\#"<<i+1<<" is "<<ar[i] << endl;
}
void Reverse_Array(double ar[], int size)
{
cout << "Now we reverse the whole array: " << endl;
for (int i = 0; i != size / 2; ++i)
{
double temp;
temp = ar[i];
ar[i] = ar[size - 1 - i];
ar[size - 1 - i] = temp;
}
}
void Reverse_Positions(double ar[], int size)
{
cout << "Enter two positions: " << endl;
int a, b;
if (cin >> a >> b)
{
double temp = ar[b - 1];
ar[b - 1] = ar[a - 1];
ar[a - 1] = temp;
}
}
Something wrong with reverse_position function: It only shows "Enter two positions" and then the function terminates. There is no chance for me to enter the integers a and b. I doubt there is something wrong with the input queue, but I am not sure.