栈的应用——计算表达式
挺久之前写的一个作业，ACM选修课的，用栈实现的计算表达式，有两种，一种是将表达式转换为后缀表达式再计算，一种是直接计算中缀表达式，下面是代码。
（1）转后缀再计算：
#include<stack>
#include<iostream>
using namespace std;
int main()
{
stack <char> s1;
stack <int> s2;
int i=0,s,v1,v2,v3;
char p[50];
cin.getline(p,50);
cout<<'=';
while(p[i]!='\0')
{
s=0;
switch(p[i])
{
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
while( (p[i]>='0') && (p[i]<='9') )
{
s=s*10+(p[i]-'0');
i++;
}
s2.push(s);
i--;
break;
case '+':
case '-':
if( (s1.empty()) || (s1.top()=='(') )
s1.push(p[i]);
else
{
while( (!s1.empty()) && (s1.top()!='(') )
{
switch(s1.top())
{
case '+':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1+v2;
s2.push(v3);
break;
case '-':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2-v1;
s2.push(v3);
break;
case '*':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1*v2;
s2.push(v3);
break;
case '/':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2/v1;
s2.push(v3);
break;
}//switch
s1.pop();
}//while
s1.push(p[i]);
}//else
break;
case '*':
case '/':
if( (s1.empty()) || (s1.top()=='(') || (s1.top()=='+') || (s1.top()=='-') )
s1.push(p[i]);
else
{
while( (!s1.empty()) && (s1.top()!='(') && (s1.top()!='+') && (s1.top()!='-') )
{
switch(s1.top())
{
case '*':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1*v2;
s2.push(v3);
break;
case '/':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2/v1;
s2.push(v3);
break;
}
s1.pop();
}
s1.push(p[i]);
}
break;
case '(':
s1.push(p[i]);
break;
case ')':
while( (!s1.empty()) && (s1.top()!='(') )
{
switch(s1.top())
{
case '+':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1+v2;
s2.push(v3);
break;
case '-':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2-v1;
s2.push(v3);
break;
case '*':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1*v2;
s2.push(v3);
break;
case '/':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2/v1;
s2.push(v3);
break;
}
s1.pop();
}
if(!s1.empty())//pop掉左括号
s1.pop();
break;
}//switch
i++;
}//while
while(!s1.empty())
{
switch(s1.top())
{
case '+':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1+v2;
s2.push(v3);
break;
case '-':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2-v1;
s2.push(v3);
break;
case '*':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1*v2;
s2.push(v3);
break;
case '/':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2/v1;
s2.push(v3);
break;
}//switch
s1.pop();
}//while
v3=s2.top();
s2.pop();
cout<<v3<<endl;
return 0;
}
输入： 55+34*（3*（3+6））-12
55+34*(3*(3+6))-12 55 34 3 3 6 + * * + 12 -=961 Press any key to continue
（2）中缀直接计算
include<stack>
#include<iostream>
using namespace std;
int main()
{
stack <char> s1;
stack <int> s2;
int i=0,s,v1,v2,v3;
char p[50];
cin.getline(p,50);
cout<<'=';
while(p[i]!='\0')
{
s=0;
switch(p[i])
{
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
while( (p[i]>='0') && (p[i]<='9') )
{
s=s*10+(p[i]-'0');
i++;
}
s2.push(s);
i--;
break;
case '+':
case '-':
if( (s1.empty()) || (s1.top()=='(') )
s1.push(p[i]);
else
{
while( (!s1.empty()) && (s1.top()!='(') )
{
switch(s1.top())
{
case '+':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1+v2;
s2.push(v3);
break;
case '-':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2-v1;
s2.push(v3);
break;
case '*':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1*v2;
s2.push(v3);
break;
case '/':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2/v1;
s2.push(v3);
break;
}//switch
s1.pop();
}//while
s1.push(p[i]);
}//else
break;
case '*':
case '/':
if( (s1.empty()) || (s1.top()=='(') || (s1.top()=='+') || (s1.top()=='-') )
s1.push(p[i]);
else
{
while( (!s1.empty()) && (s1.top()!='(') && (s1.top()!='+') && (s1.top()!='-') )
{
switch(s1.top())
{
case '*':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1*v2;
s2.push(v3);
break;
case '/':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2/v1;
s2.push(v3);
break;
}
s1.pop();
}
s1.push(p[i]);
}
break;
case '(':
s1.push(p[i]);
break;
case ')':
while( (!s1.empty()) && (s1.top()!='(') )
{
switch(s1.top())
{
case '+':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1+v2;
s2.push(v3);
break;
case '-':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2-v1;
s2.push(v3);
break;
case '*':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1*v2;
s2.push(v3);
break;
case '/':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2/v1;
s2.push(v3);
break;
}
s1.pop();
}
if(!s1.empty())//pop掉左括号
s1.pop();
break;
}//switch
i++;
}//while
while(!s1.empty())
{
switch(s1.top())
{
case '+':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1+v2;
s2.push(v3);
break;
case '-':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2-v1;
s2.push(v3);
break;
case '*':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v1*v2;
s2.push(v3);
break;
case '/':
v1=s2.top();
s2.pop();
v2=s2.top();
s2.pop();
v3=v2/v1;
s2.push(v3);
break;
}//switch
s1.pop();
}//while
v3=s2.top();
s2.pop();
cout<<v3<<endl;
return 0;
}
输入： 55+34*（3*（3+6））-12
55+34*(3*(3+6))-12 =961 Press any key to continue