为什么我的代码会RE

#include<bits/stdc++.h>
using namespace std;
string a,b;
int num;
int main(){
	char cnt;
	string s,ans;
	while(scanf("%s",&cnt) != EOF){
		if(cnt == '['){
			scanf("%d",&num);
			char cnt2;
			while(scanf("%s",&cnt2) != EOF){
				if(cnt2 == ']')cout<<ans;
				else ans+=cnt2;
			}
			while(num--)ans+=s;
		}
		else if(cnt == ']')cout<<ans;
		else ans+=cnt;
	}
	return 0;
}