逆波兰表达式实现

#include<iostream>
#include<stack>

using namespace std;

//把一个算式先转化为逆波兰表达式

int Priority(char ch)//定义优先级别
{
int i;
switch (ch)
{
case'(':i = 1; break;
case'+':i = 2; break;
case'-':i = 2; break;
case'*':i = 4; break;
case'/':i = 4; break;
case')':i = 5; break;//优先级最高
default:i = -1; break;
}
return i;
}
void tonibolan(char *ch, char retch[100])
{
stack<char> st2;
int i = 0;
while (*ch != '\0')
{
if (*ch >= '0'&&*ch <= '9')
retch[i++] = *ch;
else if (*ch == '(')//左括号直接压栈 ，不考虑优先级
st2.push(*ch);
else if (*ch == ')')//找到匹配的左括号
{
while (st2.top() != '(')
{
retch[i++] = st2.top();
st2.pop();
}
st2.pop();
}
else if (st2.empty() || Priority(*ch)>Priority(st2.top()))
st2.push(*ch);
else
{
while (Priority(*ch) <= Priority(st2.top()))
{
retch[i++] = st2.top();
st2.pop();
if (st2.empty())
break;
}
st2.push(*ch);
}
ch++;
}

while (!st2.empty())
{
retch[i++] = st2.top();
st2.pop();
}
retch[i] = 0;
}

//计算逆波兰表达式的值

int calcval(char *ret)
{

stack<char> st;
while (*ret != '\0')
{
if (*ret >= '0'&&*ret <= '9')
st.push(*ret);//数字直接入栈
else
{
switch (*ret)
{
case'+':
{
char a = st.top();
st.pop();
char b = st.top();
st.pop();
st.push(((a - '0') + (b - '0') + '0'));//注意类型的运算
break;
}
case'-':
{
char a = st.top();
st.pop();
char b = st.top();
st.pop();
st.push(((b - '0') - (a - '0')) + '0');
break;
}
case'*':
{
char a = st.top();
st.pop();
char b = st.top();
st.pop();
st.push(((b - '0')*(a - '0')) + '0');
break;
}
case'/':
{
char a = st.top();
st.pop();
char b = st.top();
st.pop();
if (a != '0')
{
st.push((((b - '0') / (a - '0')) + '0'));
}
else
{
cout << "除数为0错误" << endl;
}
break;
}
}
}
ret++;
}

return st.top() - '0';
}

int main()
{
char c;
int i = 0;
char ret[100] = {'\0'};
char ch[100] = {'\0'};
while (cin >> c)
ch[i++] = c;
tonibolan(ch, ret);

i = 0;
cout << "算式的逆波兰表达式为：" << endl;
while (ret[i]!='\0')
{
cout << ' ' << ret[i++];
}

cout << "\n算式的计算结果为：" << endl;
cout << calcval(ret) << endl;

system("pause");
return 0;
}