ff14切换快捷栏的宏:这个程序运行“找错的地方"一直是“{”，请教怎么改动程序使得括号匹配成功且报错在哪儿也成功

#include <iostream>
#include <stack>
#include <stdio.h>
using namespace std;
int main()
{
char ch;
char str[2000];
int i;
stack<int> st;
st.push(0);
cout<<"Please put an expression:"<<endl;
cin>>str;
for(i=0;i<2000;i++)
{
ch=str[i];
bool match=true;
if(ch=='{'||ch=='('||ch=='[')
switch(ch)
{
case'{':st.push(1);break;
case'(':st.push(2);break;
case'[':st.push(3);break;
}
if(ch=='}'||ch==')'||ch==']')
if(st.top()==0){
cout<<"Unmatched closing bracket"<<ch<<"detected."<<endl;
match=false;
}
else{
int m;
switch(ch)
{
case'}':m=st.top();st.pop();break;
case')':m=st.top();st.pop();break;
case']':m=st.top();st.pop();break;
}
match=(m==1&&ch=='}')
||(m==2&&ch==')')
||(m==3&&ch==']');
if(!match)
cout<<"Bad match "<<ch<<endl;
}}

if(st.top()!=0){
cout<<"Unmatched opening bracket(s) detected."<<endl;
}
else cout << "Correct!"<< endl;
system("pause");
}