Ok so for this assignment I have to have integer input in string and convert to integer..done:

int n, digit;

	cout << "Enter a number: ";
	cin >> snum;
	n = 0;
	int power = pow(10, snum.length()-1);
	for (int i=0; i<snum.length(); i++)
	{	digit = snum.at(i) - '0';
		n = n + digit*power;
		power = power/10;

	cout << "n is "<< n <<endl;

then: convert the number to a decimal number from which ever base the user inputs.

Thats where I am lost, I have no idea where to start. Please help!!

How would you do it on paper? What are the exact steps? Write the steps down. If that doesn't help completely, ask specific questions about the steps.