一个用栈实现的括号匹配

#include<iostream>
#include<cstring>
#include<stack>
using namespace std;


int main(){
    string input;
    cin>>input;
    int a=input.length();
    stack <char> stk;
    if(a%2 != 0){
        cout<<"False"<<endl;
        return 0;
    }
    for(int i=0;i<a;i++){
        char ch = input[i];
        if(ch == '{' || ch == '(' || ch =='['){
            stk.push(ch);
        }
        else{
            if(ch=='}'){
                if(stk.top() == '{'){
                    stk.pop();
                }
                else{
                    cout<<"False"<<endl;
                    return 0;
                }
            }
            if(ch==']'){
                if(stk.top() == '['){
                    stk.pop();
                }
                else{
                    cout<<"False"<<endl;
                    return 0;
                }
            }
            if(ch==')'){
                if(stk.top() == '('){
                    stk.pop();
                }
                else{
                    cout<<"False"<<endl;
                    return 0;
                }
            }
        }
    }
    if(stk.empty()){
        cout<<"True"<<endl;
    }
    else{
        cout<<"False"<<endl;
    }
    return 0;
}