传统意义的四舍五入计算

看看net的四舍五入：

  static void Main(string[] args)
        {
            Console.WriteLine(Math.Round(1.015, 2));
            Console.WriteLine(Math.Round(1.0151, 2));
            Console.WriteLine(Math.Round(1.0149, 2));
  
            Console.ReadLine();
        }

Output:

1.01
1.02
1.01

可以看出不是我们想要的四舍五入。

Code:

    /// <summary>
        /// 四舍五入计算
        /// </summary>
        /// <param name="value"></param>
        /// <param name="digit"></param>
        /// <returns></returns>
        public double Round(double value, int digit = 0)
        {
            return Round(Convert.ToDecimal(value), digit);
        }

        public double Round(decimal value, int digit = 0)
        {
            decimal vt = Convert.ToDecimal(Math.Pow(10, digit));
            //1.乘以倍数 + 0.5
            decimal vx =  value * vt + 0.5m;
            //2.向下取整
            decimal temp = Math.Floor(vx);
            //3.再除以倍数
            return Convert.ToDouble(temp / vt);
        }

    static void Main(string[] args)
        {
            Console.WriteLine(Round(1.015, 2));
            Console.WriteLine(Round(1.0151,2));
            Console.WriteLine(Round(1.0149, 2));
 
            Console.ReadLine();
        }

Output:

1.02
1.02
1.01

C#用double,float浮点计算会有误差，所以切换成decimal计算。

=============================================================================

Js端：

toFixed

console.log(1.049.toFixed(2));
console.log(1.054.toFixed(2));
console.log(1.055.toFixed(2));
console.log(1.056.toFixed(2));
VM224:1 1.05
VM224:2 1.05
VM224:3 1.05
VM224:4 1.06

发现1.055错误

Math.round

console.log(Math.round(1.049*100)/100);
console.log(Math.round(1.054*100)/100);
console.log(Math.round(1.055*100)/100);
console.log(Math.round(1.059*100)/100);
VM309:1 1.05
VM309:2 1.05
VM309:3 1.06
VM309:4 1.06

OK

code:

  function Round(value, digit)
        {
            if(!digit)digit=0;
            var vt =  Math.pow(10, digit);
            //1.乘以倍数 + 0.5
            var vx = value  * vt + 0.5;
            //2.向下取整
            var temp = Math.floor(vx);
            //3.再除以倍数
            return  temp / vt;
        }

=================================================

js的浮点计算：

http://blog.csdn.net/qinshenxue/article/details/43671763