poj2106——Boolean Expressions

题意：求表达式运算

思路：同数字表达式运算一样，先转后缀，再求值。

注意点：1，'('在进栈时，优先级最高，出栈时相反；

            2，对于'!'，单目表达式的计算，在转后缀的时候，需将数值进栈，再将其压入后缀表达式中；

#include<cstdio>#include<cstring>#include<iostream>using namespace std;const int len =120; char infix[len],suffix[len];void infixtosuffix(){int top=-1,i=0,j=0;char ch=infix[0],stk[len];while(ch!='/0'){if(ch==' '){}else if(ch=='('){top++;stk[top]=ch;}else if(ch==')'){while(stk[top]!='('){suffix[j++]=stk[top];top--;}top--;}else if(ch=='!'){top++;stk[top]=ch;}else if(ch=='&'){while(stk[top]=='&'||stk[top]=='!'){suffix[j++]=stk[top];top--;}top++;stk[top]=ch;}else if(ch=='|'){while(top!=-1&&stk[top]!='('){suffix[j++]=stk[top];top--;}top++;stk[top]=ch;}else{suffix[j++]=ch;while(top!=-1&&stk[top]=='!'){suffix[j++]=stk[top];top--;}}ch=infix[++i];}while(top!=-1){suffix[j++]=stk[top];top--;}suffix[j++]='/0';}void pri_result(){int i=0,top=-1;char ch=suffix[i];bool result[len];while(ch!='/0'){if(ch=='F'){top++;result[top]=false;}else if(ch=='V'){top++;result[top]=true;}else if(ch=='!')result[top]=!result[top];else if(ch=='|'){result[top-1]|=result[top];top--;}else if(ch=='&'){result[top-1]&=result[top];top--;}ch=suffix[++i];}if(result[top]==true)printf("V/n");else printf("F/n");}int main(){int i=1;while(cin.getline(infix,len)){infixtosuffix();printf("Expression %d: ",i++);pri_result();}return 0;}