为什么这样写编译错误

#include<iostream>
#include<cstdio>
using namespace std;
int main(){
    cout<<('O'-'I')| 4;
}

但这样写能通过

```cpp
#include<iostream>
#include<cstdio>
using namespace std;
int main(){
    cout<<('O'-'I')|| 4;
}

而且输出6