小白求教，会WA掉几个点

#include<cstdio>
#include<iostream>
#include<cstring>
#include<stack>
#include<algorithm>
using namespace std;
char c[105],b[105];
stack<char> s;
int main(){
    scanf("%s",c);
    int len=strlen(c);
    for(int i=0;i<len;i++){
        if(c[i]=='('){s.push(i);b[i]=')';}
        else if(c[i]=='['){s.push(i);b[i]=']';}

        else if(!s.empty()){     //Åöµ½£©] 
            if(c[s.top()]=='('&&c[i]==')'){
                b[s.top()]='*';
                s.pop();
                b[i]='*';
            }
            else if(c[s.top()]=='['&&c[i]==']'){
                b[s.top()]='*';
                b[i]='*';
                s.pop();
            }
        }
        else {
        if(c[i]==')'){b[i]='(';}
        else if(c[i]==']'){b[i]='[';}   

        }
    }

    for(int i=0;i<len;i++){
        if(b[i]=='*'){
            printf("%c",c[i]);
        }else if(c[i]=='('||c[i]=='['){
            printf("%c",c[i]);
            printf("%c",b[i]);
        }else if(c[i]==')'||c[i]==']'){
            printf("%c",b[i]);
            printf("%c",c[i]);

        }
    }
    return 0;
}