public string EvaluateExpression(string expressions)
{//计算表达式
expressions = expressions + '#';
//存储运算值的栈
myStack operation = new myStack();
operation.Push(0);
//存储运算符的栈
myStack TR = new myStack();
TR.Push('#');
char c, theta;
char[] num = new char[20];
int j = 0;
for (int i = 0; i < expressions.Length; i++)
{
c = Convert.ToChar(expressions[i]);
int a, b;
if (Char.IsDigit(c))
{
num[j++] = c;
continue;
}
else
{
if (j != 0)
{
num[j] = Convert.ToChar(0); operation.Push(strToNum(num)); j = 0;
}
switch (CompareTR(TR, c))
{
case '<': { TR.Push(c); break; }
case '>':
{
theta = Convert.ToChar(TR.Pop());
b = Convert.ToInt32(operation.Pop()); a = Convert.ToInt32(operation.Pop());
operation.Push(Operate(a, theta, b));
break;
}
case '=': { c = Convert.ToChar(TR.Pop()); break; }
}
}
}
return(Convert.ToString(operation.Pop()));
}
private char CompareTR(myStack S, char c)
{//判断优先级
char iResult = ' ';
switch (S.GetTop())
{
case '+':
{
if (c == '*' || c == '/' || c == '(')
{
return('<');
}
else if (c == '+' || c == '-' || c == ')' || c == '#')
{
return('>');
}
break;
}
case '-':
{
if (c == '*' || c == '/' || c == '(')
{
return('<');
}
else if (c == '+' || c == '-' || c == ')' || c == '#')
{
return('>');
}
break;
}
case '*':
{
if (c == '(')
{
return('<');
}
else if (c == '+' || c == '-' || c == '*' || c == '/' || c == ')' || c == '#')
{
return('>');
}
break;
}
case '/':
{
if (c == '(')
{
return('<');
}
else if (c == '+' || c == '-' || c == '*' || c == '/' || c == ')' || c == '#')
{
return('>');
}
break;
}
case '(':
{
if (c == ')')
{
return('=');
}
else
{
return('<');
}
break;
}
case ')':
{
return('>');
break;
}
case '#':
{
if (c == '#')
{
return('=');
}
else
{
return('<');
}
break;
}
}
return(iResult);
}