/// <summary>
/// 利用Excel中VBA的Evaluate方法对字符串进行解析计算
/// </summary>
/// <param name="str"></param>
/// <returns></returns>
public static double Cal(this string str)
{
var app = new Excel.Application();
Excel.Workbook workbook = app.Workbooks.Add();
Excel.Worksheet worksheet = workbook.Worksheets.Add() as Excel.Worksheet;
var result = worksheet.Evaluate(str);
app.DisplayAlerts = false;
app.Quit();
if (double.Parse(result.ToString()) <0)
{
return 0;
}
else
{
return double.Parse(result.ToString());
}
}