I have no clue how to make intSum = 0; in the loop, so everytime you have clean variables.
Just assign it zero here. You will also have to assign 1 to intPowr also.
if (intNumb == 0)
cout << "Sum of digits is :" << intSum << endl; // displays result when int = 0
cout << "Enter an integer number (o to stop): ";
cin >> intInpt;
intSum = 0; // Reinitialize
intPowr = 1; // Reinitialize