大佬帮看一下what happen 导致这段代码凯撒密码翻译失败—

#include<bits/stdc++.h>
using namespace std;
int main( ){
	int y;
	cin>>y;
	char a[y];
		for(int i=0;i<sizeof(a);i++){
		cin>>a[y];
	} 
	
	for(int i=0;i<y;i++){
		cout<<a[i]+1<<"/";
	} 
	cout<<"\nEnter to the secret";
}