Question

I am working on a programming assignment in which we are making our own BigNum class. One of the constructors needs to be set up so that it can take a number from a string (i.e. 342567) and reads it into an array. However if the number were 0000000342567 it would have to be able to skip over the 0s and just read 342567.

Where is what i have so far but am lost on trimming the 0s

BigNum::BigNum(const char strin[])
{
    size_t size = strlen(strin);
    positive = true;
    capacity = size;
    digits = new size_t[capacity];
    used=0;

    while(used<size)
    {
        if(strin[size - used -1] =='-')
        {
            positive = false;
            size --;
        }
        else if(strin[size - used -1] =='+')
        {
            size --;
        }
        else
        {
            digits[used] = strin[size - used -1] - '0';
            used++;
        }
    }
}

Here is the assignment description if it helps
http://csel.cs.colorado.edu/%7Eekwhite/CSCI2270Fall2011/hw2/Homework2.pdf

Answer 1

Add this just before your while loop:

for (int i=0; i < size; i++)
{
    if (strin[i] >= '1' && strin[i] <= '9')
    {
        used = i;
        break;
    }
}

This way, your while loop begins reading the string only from the index where the number actually begins, skipping over all leading 0s.

This should handle the leading sign as well:

BigNum::BigNum(const char strin[])
{
    size_t size = strlen(strin);
    positive = true;        
    used=0;

    if (strin[0] == '+' || strin[0] == '-')
    {
        //set positive or negative
        used++;
    }
    while (used < size)
    {
        if (strin[used] != '0')     
            break;

        used++; //used will only increment if above if condition failed.
    }

    int digitIndex = 0;
    digits = new size_t[size-used]; //create digits array here so it isn't larger than needed

    while(used<size)
    {        
         digits[digitIndex++] = strin[used++];      
    }
}