/// <summary>
/// operator + overloaded
/// addtion of 2 bignumber can use + now
/// write the oprands and result to the screen
/// return a sum bignumber
/// </summary>
/// <param name="op1">LHS oprand</param>
/// <param name="op2">RHS oprand</param>
/// <returns>sum bignumber</returns>
public static BigNumber operator +(BigNumber op1, BigNumber op2)
{
if (op1.IsEmpty() && op2.IsEmpty())
{
return(null);
}
else if (op1.IsEmpty())
{
return(op2);
}
else if (op2.IsEmpty())
{
return(op1);
}
else
{
int sum;
int carry = 0;
var current1 = op1.First;
var current2 = op2.First;
var result = new BigNumber();
//if any of those 2 still have digits, looping
while (current1 != null || current2 != null)
{
//reset sum to 0 every turn of loop
//take the carry value from last turn
sum = 0;
//if available add current value to the sum
//Char.GetNumericValue returns int of char's literal value
//thus it does not need to go through ASCII conversion
if (current1 != null)
{
sum += (int)Char.GetNumericValue(current1.Value);
current1 = current1.Next;
}
if (current2 != null)
{
sum += (int)Char.GetNumericValue(current2.Value);
current2 = current2.Next;
}
//add carry to sum, last turn carry now expired
sum += carry;
//new carry and new sum
carry = sum / 10;
sum = sum % 10;
//add sum to the list
//sum must add 48 according to ASCII table to make a char's literal is this sum
//AddLast because need to make sure lower digits are at LHS of the list
result.AddLast((char)(sum + 48));
}
//if carry is not zero, and a new node in the list represent 1
if (carry == 1)
{
result.AddLast((char)49);
}
//print result to screen
op1.Write();
Console.WriteLine("+");
op2.Write();
Console.WriteLine("=");
result.Write();
return(result);
}
}