Question

我正在尝试使用向量进行非常大的乘法，并且在运行算法时我一直遇到问题。

vector<vector<int>> finalresult;
vector<int> currentrow;
int carry=0, workingnum=0, innerval =0, curnt=0, j=0;

for (auto an = a.rbegin(); an != a.rend(); ++an)
{
    for (auto bn = b.rbegin(); bn != b.rend(); ++bn)
    {
        curnt = (*an) * (*bn);
        if (curnt > 10 && carry ==0)
        {
            carry = curnt / 10;
            currentrow.push_back(curnt % 10);
        }
        if (curnt < 10 && carry ==0)
        {
            currentrow.push_back(curnt);
        }
        if (curnt < 10 && carry >0)
        {
            if ((curnt + carry) < 10)
            {
                currentrow.push_back(curnt + carry);
            }
            else
            {
                workingnum = curnt + carry;
                carry = workingnum / 10;
                currentrow.push_back(workingnum % 10);
            }
        }
        else
        {
            workingnum = curnt + carry;
            carry = workingnum / 10;
            currentrow.push_back(workingnum % 10);
        }

    }
    finalresult.push_back(currentrow);
    for (int i = 0; i < currentrow.capacity(); i++)
    {
        currentrow.pop_back();
    }
    for (int i=0; i < j; i++)
    {
        currentrow.push_back(0);
    }
    j++;
}

每次运行此代码时，如果它遇到内部if语句之一，如curnt＆lt; 10和carry == 0，它会push_back弯曲，但是然后它也会在else部分再次执行。我无法理解为什么它也会在其他部分发生。（我知道那是因为调试而发生的事情）任何人都可以对此有所了解吗？

Answer 1

你有：

if (curnt < 10 && carry >0)
{
    if ((curnt + carry) < 10)
    {
        currentrow.push_back(curnt + carry);
    }
    else
    {
        workingnum = curnt + carry;
        carry = workingnum / 10;
        currentrow.push_back(workingnum % 10);
    }
}
else
{
    workingnum = curnt + carry;
    carry = workingnum / 10;
    currentrow.push_back(workingnum % 10);
}

无论您在if行之前执行了什么操作，都会执行else块或if块。

<强>简化

您可以替换

if (curnt > 10 && carry ==0)
{
   carry = curnt / 10;
   currentrow.push_back(curnt % 10);
}
if (curnt < 10 && carry ==0)
{
   currentrow.push_back(curnt);
}
if (curnt < 10 && carry >0)
{
   if ((curnt + carry) < 10)
   {
      currentrow.push_back(curnt + carry);
   }
   else
   {
      workingnum = curnt + carry;
      carry = workingnum / 10;
      currentrow.push_back(workingnum % 10);
   }
}
else
{
   workingnum = curnt + carry;
   carry = workingnum / 10;
   currentrow.push_back(workingnum % 10);
}

通过

curnt += carry;
carry = curnt / 10;
currentrow.push_back(curnt % 10);

如何使用vectors <int>进行极大的整数乘法</int>

1 个答案: