数据结构实验 第二单元 构造计算器

/// <summary>
/// 将前缀表达式转换为后缀表达式
/// </summary>
/// <param name="strInfix"></param>
/// <returns></returns>
private string InfixToSuffix(string strInfix)
{
LinkStack ls = new LinkStack();
System.Text.StringBuilder sb = new StringBuilder(200);
string str = strInfix.Trim();
foreach(var word in str)
{
if (char.IsNumber(word))
{
sb.Append(word);
}
else
{
//非数字，先加个空格。
sb.Append(' ');
if (word == '(')
{
ls.Push(word);
}
else if (word == ')')
{
while (!ls.Empty())
{
char ch = (char)ls.Pop();

if (ch == '(')
{
break;
}
sb.Append(ch);
}
}
else if (word == '+' || word == '-')
{
while(!ls.Empty())
{
char ch = (char)ls.Top();
if (ch == '+' || ch == '-' || ch == '*' || ch == '/')
{
sb.Append((char)ls.Pop());
}
else if (ch == '(')
{
break;
}
}
ls.Push(word);
}
else if (word == '*' || word == '/')
{
while (!ls.Empty())
{
char ch = (char)ls.Top();
if (ch == '*' || ch == '/')
{
sb.Append((char)ls.Pop());
}
else if (ch == '+' || ch == '-' || ch == '(')
{
break;
}
}
ls.Push(word);
}
else
{

}
}
}
while (!ls.Empty())
{
sb.Append(ls.Pop());

}
return sb.ToString();
}

/// <summary>
/// 计算后缀表达式
/// </summary>
/// <param name="strSuffix"></param>
/// <returns></returns>
private int CalculateSuffix(string strSuffix)
{
LinkStack ls = new LinkStack();
int num=0;
Boolean numState = false;
foreach (var word in strSuffix)
{
if (char.IsNumber(word))
{
numState = true;
num = num*10+int.Parse(word.ToString());
}
else
{
//将数入栈
if (numState == true)
{
ls.Push(num);
num = 0;
}
numState=false;
if (word != ' ')
{
//忽略空白
int num2 = (int)ls.Pop(), num1 = (int)ls.Pop();
switch(word)
{
case '+':
ls.Push(num1 + num2);
break;
case '-':
ls.Push(num1 - num2);
break;
case '*':
ls.Push(num1 * num2);
break;
case '/':
ls.Push(num1 / num2);
break;
}
}
}
}

return (int)ls.Pop();
}