Question

This loop is supposed to add two numbers that are stored in vectors by their individual digits. So, for example leftc will contain [10]{0,9,0,0,0,0,0,0,5,7} and rightc will contain
[10]{0,0,0,0,0,0,0,0,9,6} and at the end of the loop number should contain “0900000153” (leading zeros are stripped off later in the program). It works perfectly until it gets to index = 0 and then it causes an overflow error, but I can’t figure out why.

string number;                                                      // accumulates the result of the addition
int num;                                                            // holds the result of adding corresponding elements
short carry = 1;

for ( size_t index = leftc.size() - 1; index >= 0; index-- )        // start from the end of the vectors and work toward the beginning
{
    num = leftc.at(index) + rightc.at(index);                       // add the two elements and store in num
    if ( num >= 10 )
    {
        num %= 10;
        leftc.at(index - 1) += carry;
    }
    num += '0';                                                     // convert num from int to char                                             
    number.insert( number.begin(), num );                           // store num at front of number
}

Any help is greatly appreciated. Thank you!

Answer 1

You have a problem here

for ( size_t index = leftc.size() - 1; index >= 0; index-- ) 

As size_t is unsigned, index will always be >=0.