How to get the sum of two strings of numbers - C++

Question

How do I get the sum of two strings that are numbers? For example:

string num1 = "12";
string num2 = "4";

string sum = num1 + num2;

So string sum will equal "16"

How do I do this in c++?

I tried doing it with ascii characters but it does not work I cannot convert the string to an integer as well

Answer 1

To add large integers using string, you can do something like this.

string doSum(string a, string b)
{
    if(a.size() < b.size())
        swap(a, b);

    int j = a.size()-1;
    for(int i=b.size()-1; i>=0; i--, j--)
        a[j]+=(b[i]-'0');

    for(int i=a.size()-1; i>0; i--)
    {
        if(a[i] > '9')
        {
            int d = a[i]-'0';
            a[i-1] = ((a[i-1]-'0') + d/10) + '0';
            a[i] = (d%10)+'0';
        }
    }
    if(a[0] > '9')
    {
        string k;
        k+=a[0];
        a[0] = ((a[0]-'0')%10)+'0';
        k[0] = ((k[0]-'0')/10)+'0';
        a = k+a;
    }
    return a;
}

int main()
{
    string result = doSum("1234567890", "123789456123");
    cout << result << "\n";
}

Output

125024024013

Reference: See the complete code at Ideone.com