后缀表达式

#include <stdio.h>#include "sqstack.h"#define MaxOp 7struct  //设定运算符优先级{char ch;   //运算符int pri;   //优先级}lpri[]= {{'=',0},{'(',1},{'*',5},{'/',5},{'+',3},{'-',3},{')',6}},rpri[]= {{'=',0},{'(',6},{'*',4},{'/',4},{'+',2},{'-',2},{')',1}};int leftpri(char op)    //求左运算符op的优先级{int i;for (i=0; i<MaxOp; i++)if (lpri[i].ch==op)return lpri[i].pri;}int rightpri(char op)  //求右运算符op的优先级{int i;for (i=0; i<MaxOp; i++)if (rpri[i].ch==op)return rpri[i].pri;}bool InOp(char ch)       //判断ch是否为运算符{if (ch=='(' || ch==')' || ch=='+' || ch=='-'|| ch=='*' || ch=='/')return true;elsereturn false;}int Precede(char op1,char op2)  //op1和op2运算符优先级的比较结果{if (leftpri(op1)==rightpri(op2))return 0;else if (leftpri(op1)<rightpri(op2))return -1;elsereturn 1;}void trans(char *exp,char postexp[])//将算术表达式exp转换成后缀表达式postexp{SqStack *opstack;               //定义运算符栈int i=0;                //i作为postexp的下标ElemType ch;InitStack(opstack);   //用初始化栈运算为栈分配空间，务必要做Push(opstack, '=');while (*exp!='\0')      //exp表达式未扫描完时循环{if (!InOp(*exp))        //为数字字符的情况{while (*exp>='0' && *exp<='9') //判定为数字{postexp[i++]=*exp;exp++;}postexp[i++]='#';   //用#标识一个数值串结束}else    //为运算符的情况{GetTop(opstack, ch);   //取得栈顶的运算符switch(Precede(ch ,*exp)){case -1:           //栈顶运算符的优先级低:进栈Push(opstack, *exp);exp++;     //继续扫描其他字符break;case 0:        //只有括号满足这种情况Pop(opstack, ch);      //将(退栈exp++;     //继续扫描其他字符break;case 1:             //退栈并输出到postexp中postexp[i++]=ch;Pop(opstack, ch);break;}}} //while (*exp!='\0')Pop(opstack, ch);while (ch!='=')//此时exp扫描完毕,退栈到'='为止{postexp[i++]=ch;Pop(opstack, ch);}postexp[i]='\0';    //给postexp表达式添加结束标识DestroyStack(opstack);}int main(){char exp[]="(56-20)/(4+2)"; //可将exp改为键盘输入char postexp[200];trans(exp,postexp);printf("中缀表达式:%s\n",exp);printf("后缀表达式:%s\n",postexp);return 0;}