Start New Discussion within our **Software Development Community** # BigInteger addition

```
#include <iostream>
#include <string>
using namespace std;
struct DigitPair
{
unsigned digitA;
unsigned digitB;
DigitPair() {
digitA = 0;
digitB = 0;
}
};
class DigitIterator
{
private:
string s1;
string s2;
int pos1;
int pos2;
public:
DigitIterator(const string &str1, const string &str2) {
s1 = str1;
s2 = str2;
pos1 = s1.length() - 1;
pos2 = s2.length() - 1;
}
DigitPair nextDigits() {
DigitPair dp;
if ( pos1 >= 0 )
dp.digitA = s1[ pos1-- ] - '0';
if ( pos2 >= 0 )
dp.digitB = s2[ pos2-- ] - '0';
return dp;
}
bool hasDigits() {
return ( pos1 >= 0 || pos2 >= 0 );
}
};
string add(string &n1, string &n2);
int main()
{
string n1, n2;
cout << "Enter two integers: ";
cin >> n1 >> n2;
cout << n1 << " + " << n2 << " = ";
cout << add(n1, n2) << endl;
}
string add(string &n1, string &n2)
{
DigitIterator iter(n1, n2);
string result;
bool carry = false;
while ( iter.hasDigits() || carry )
{
DigitPair dp;
dp = iter.nextDigits();
int sum = dp.digitA + dp.digitB;
if ( carry )
{
sum++;
carry = false;
}
if ( sum > 9 )
{
sum = sum - 10;
carry = true;
}
result = (char)(sum + '0') + result;
}
return result;
}
```

The article starter has earned a lot of community kudos, and such articles offer a bounty for quality replies.