C/C++ 浮點數[精度問題]~四捨五入函數

 

資料來源:https://github.com/jash-git/Statistics_CPP_project/blob/master/01_frequency_distribution_table/CLib.cpp

 

// 四捨五入 取到 小數點第 X 位
double CLib::rounding(double num, int index)
{
    //https://dotblogs.com.tw/forloop/2016/07/31/rounding
    bool isNegative = false; // whether is negative number or not

    if(num < 0) // if this number is negative, then convert to positive number
    {
        isNegative = true;
        num = -num;
    }

    if(index >= 0)
    {
        int multiplier;
        multiplier = pow(10, index);
        num = (int)(num * multiplier + 0.5) / (multiplier * 1.0);
    }

    if(isNegative) // if this number is negative, then convert to negative number
    {
        num = -num;
    }

    return num;
}