/**
* 后缀表达式求值运算
*/
public String getResult()
{
getBackExpression();
String operator1, operator2, tmp;
int index = 0;
DefineStack ds = new DefineStack();
//String first = (String)ienumerator.Current;
while (index < backExpression.Count)
{
tmp = (String)backExpression[index];
//将栈顶两个操作数出栈，计算二者的值
index++;
if (CalculateUtil.isOperator(tmp))
{
operator1 = (String)ds.pop();
operator2 = (String)ds.pop();
String tmpResult = CalculateUtil.twoOperate(tmp, operator1, operator2);
if (tmpResult.Equals("error"))
{
return("error");
break;
}
ds.push(tmpResult);
}
else
{
ds.push(tmp);
}
}
result = (String)ds.pop();
return(result);
}
/**
* 转换中缀表达式为后缀表达式算法
*/
private void getBackExpression()
{
DefineStack ds = new DefineStack();
String operators;
int position = 0;
while (true)
{
if (CalculateUtil.isOperator((String)middleExpression[position]))
{
//如果运算符为"("，直接存入运算符栈
if (ds.top == -1 || ((String)middleExpression[position]).Equals("("))
{
ds.push((String)middleExpression[position]);
}
//如果运算符是")",出操作符栈并添加到表达式顺序表中，直到遇到"("
else if (((String)middleExpression[position]).Equals(")"))
{
while (!((String)ds.getTop()).Equals("("))
{
operators = (String)ds.pop();
backExpression.Add(operators);
}
//这里需要弹出"("操作符
ds.pop();
}
//如果当前的运算符比栈顶的运算符优先级低，则输出栈顶运算符到顺序表，并将当前运算符压入运算符栈
else if (CalculateUtil.getPority((String)middleExpression[position]) <=
CalculateUtil.getPority((String)ds.getTop()) && (ds.top != -1))
{
operators = (String)ds.pop();
if (!operators.Equals("("))
{
backExpression.Add(operators);
}
ds.push((String)middleExpression[position]);
}
else
{
ds.push((String)middleExpression[position]);
}
position++;
}
//如果不是操作符，直接将操作数添加到顺序表中
else
{
backExpression.Add((String)middleExpression[position]);
position++;
}
if (position >= middleExpression.Count)
{
break;
}
}
while (ds.top != -1)
{
operators = (String)ds.pop();
backExpression.Add(operators);
}
}