C++中缀表达式怎么转后缀表达式

#include<iostream>
#include<cstring>
#include<algorithm> 
#include<stack>
using namespace std;
 
stack<char> s1; //运算符栈 
stack<char> s2; //中间结果栈 
 
int f(const char str){
 int yxj; //优先级 
 switch(str){
 case '*':yxj=5;break;
 case '/':yxj=5;break;
 case '+':yxj=4;break;
 case '-':yxj=4;break;
 }
 return yxj;
 
}
int main(){
 char c[100]="(12+4-13)+6*2";
 //char c[100]="1+((2+3)*4)-5";
 int lenc=strlen(c);
 //读取字符串 
 for(int i=0;i<lenc;i++){
 if(c[i]>='0'&&c[i]<='9'){ //如果是数字，直接压入s2 
 s2.push(c[i]);
 }else if(c[i]=='+'||c[i]=='-'||c[i]=='*'||c[i]=='/'){ //如果是运算符 
 while(true){
 if(s1.empty()||s1.top()=='('){ //s1为空 ，或者栈顶为( 
 s1.push(c[i]);
 break;
 }else if(f(c[i])>f(s1.top())){ //当前运算符优先级大于s1栈顶运算符优先级 
 s1.push(c[i]);
 break;
 }
 else{ //小于等于 
 char cc=s1.top();
 s1.pop();
 s2.push(cc);
 }
 }
 }else{
 if(c[i]=='('){ //直接读入 
 s1.push(c[i]);
 }else{
 while(s1.top()!='('){
 char ccc=s1.top();
 s1.pop();
 s2.push(ccc);
 }
 s1.pop();
 }
 }
 }
 while(!s1.empty()){
 char cccc=s1.top();
 s2.push(cccc);
 s1.pop();
 }
 
 //while(!s2.empty()){ //结果是逆序的 
 // cout<<s2.top();
 // s2.pop();
 //}
 while(!s2.empty()){
 char c=s2.top();
 s1.push(c);
 s2.pop();
 }
 while(!s1.empty()){ 
 cout<<s1.top();
 s1.pop();
 }
 
 return 0;
}